British refineries have been asked to maximise jet fuel supply as part of government contingency planning, amid growing fears the Iran war will force planes to be grounded.

Energy minister Michael Shanks said the government is closely monitoring UK jet fuel stocks and working with airlines, airports, fuel suppliers and other governments, as carriers face rocketing fuel costs as a result of the conflict.

Normal flows of fossil fuels from the Gulf have effectively been at a standstill since the war broke out, after the de facto closure of the important shipping channel, the strait of Hormuz, through which a fifth of the world’s oil and gas flows.

“UK airlines typically buy fuel months in advance, and aviation fuel suppliers hold bunkered stocks. The UK imports jet fuel supplies from a range of countries not reliant on the strait, including the United States,” wrote Shanks in a ministerial statement.

“Airlines UK have stated that ‘UK airlines continue to operate normally and are not experiencing issues with jet fuel supply.’ The government continues to work with partners to monitor and mitigate potential disruptions,” Shanks added.

There are now only four remaining refineries in the UK, after closures at the Grangemouth and Lindsey refineries in 2025.

The remaining UK refineries are: Fawley in Hampshire owned by ExxonMobil; Humber in Lincolnshire owned by Phillips 66; Valero’s Pembroke refinery in Wales; and Essar’s Stanlow site in Essex.

These sites produce a range of refined products including petrol, diesel, jet fuel and fuel oil to meet domestic demand and for export. The number of UK refineries has fallen from a peak of 18 in the 1970s, as has the UK’s output of petrol and diesel.

It came as global jet fuel shipments fell to the lowest recorded level last week. Just under 2.3m tonnes of jet fuel and kerosene were transported on ships in the seven days to 26 April, according to initial analysis by data company Kpler, which first began tracking shipments in 2017. The figure represents less than half the average weekly volume shipped before the war.

Airlines have insisted there are now no supply problems expected during their typical four-to-six week horizon, although some carriers have already announced flight cancellations, and have been lobbying for government help amid rising fuel prices and a possible supply crisis.

Airlines that cancel flights because of a lack of fuel will not lose their rights to valuable takeoff and landing slots at busy airports, which can be forfeited when flights fail to operate over a period.

It was announced on Friday that exemptions to the “use-it-or-lose-it” rule can be granted during shortages by Airport Coordination Ltd, the independent body that manages slots at UK airports, in an attempt to minimise disruption and prevent airlines from flying to protect slots.

Budget travel carrier Jet2 said on Wednesday it remained in contact with its fuel suppliers and airports.

The group said it had hedged 87% of its fuel requirement for the peak summer season, at an average price of $707 a metric tonne, giving it “a high degree of cost certainty”.

Jet2 said “current geopolitical uncertainty” over the Middle East conflict meant holidaymakers were booking trips closer to departure, making it difficult to predict bookings for the peak summer season and beyond.

Heathrow airport also told investors it was facing an “uncertain outlook” as a result of the conflict, despite reporting a short-term boost in the number of passengers travelling through the airport to change planes because of airspace closures in the Middle East.

Nearly 19 million passengers travelled through the airport during the first three months of the year, an increase of 3.7% compared with a year earlier.

Heathrow said it had “temporarily absorbed demand from elsewhere” but did not expect this to continue for the rest of the year, given “significant uncertainty” in the region.

More than 150 people convicted of violent crimes were granted taxi licences last year by Wolverhampton city council, dubbed the UK’s “taxi capital”, data has revealed.

The Guardian obtained data via a freedom of information request that revealed 438 people with criminal convictions were last year granted taxi and private hire driver licences by the West Midlands local authority – which has issued far more taxi licences than any other authority.

This included 158 people convicted of violent offences, 61 convicted of drug offences, 36 of drink offences and four of sexual offences. The council said 16 drivers had convictions in two of the requested categories.

Drivers with licences issued by Wolverhampton council can work, using apps like Uber and Bolt, in other local authority areas.

Between April 2023 and the end of March 2024, the city council issued more than than 42,000 driver licences, compared with Birmingham and Bradford, which had issued the second and third largest number of licences – more than 7,000 each – according to government data.

Wolverhampton’s extraordinary dominance of the taxi licensing system has raised concerns over safety risks to passengers, but the authority has denied claims it is quicker and easier to get a licence there.

A report by the council’s regulatory committee said it appealed to drivers due to its work to digitise its application form and streamline processes.

Several key figures have voiced concerns around inconsistent safeguarding standards in taxi licensing, with the government currently exploring proposals to reduce the number of bodies issuing licences and reduce out-of-area working, which enables drivers licensed in one area to operate in another.

Between April 2023 and the end of March, Wolverhampton council said 96% of its licensed drivers lived outside the city.

The mayor of Greater Manchester, Andy Burnham, called the figures obtained by the Guardian “truly shocking” and said they “lay bare the fundamental issue with how private hire licensing is managed in this country”.

“We want our taxis and private hire vehicles [PHVs] to be among the safest and most trusted in the country, but we can’t do this with the current broken licensing system, where local leaders have zero oversight over nearly half the PHVs on our streets,” the mayor said.

The Suzy Lamplugh Trust, which works to reduce stalking and harassment, said it has been campaigning for consistent safeguarding standards in taxi licensing since 2014 and called for drivers to be viewed as a regulated activity to ensure stricter background checks.

A spokesperson for the Department for Transport said its statutory guidance is “clear that anyone convicted of a sexual offence should not be granted a taxi or private hire licence”, adding that licensing decisions are taken by individual local authorities with reference to government guidance.

Its guidance also states that a licence should not be granted to an applicant convicted of a violent offence until at least 10 years have elapsed since the sentence was completed.

The chief executive of Wolverhampton council said “safeguarding is such a priority for us”, and each application is “scrutinised and considered” on the basis of local and national policies.

“There is nothing more important to us than the safety of passengers in cars licensed by this council,” Tim Johnson said. “We refuse thousands of licence applications each year.”

He added that Wolverhampton is the only council to carry out Disclosure and Barring Service (DBS) checks on all of its drivers and the only local authority to share data about the convictions of licensed drivers.

“Licences are only approved if our panel – which includes a trained decision maker and solicitor – would be happy for a person they care for to travel alone in a vehicle driven by this person at any time of day or night,” he said. “We know that other authorities have licensed drivers with similar previous convictions.”

Drivers with PHV licences work for companies such as Uber and Bolt, and can only carry out pre-booked journeys. Spokespeople for both companies said the decision to grant a private hire driver licence is made by a local authority and details about a driver’s background checks are not passed on to them.

“Bolt’s own data shows no meaningful link between where a driver is licensed and reported safety incidents,” a Bolt spokesperson added.

Uber and Bolt said they have introduced safety tools for passengers, including providing details about their driver’s identity and vehicle details before they get into the car.

Wolverhampton council, along with Uber and Bolt, said it supported plans to reform the taxi licensing system.

The Guardian also requested data on the number of licences issued to people with criminal convictions to Birmingham and Bradford councils.

Birmingham said it does require applicants to provide enhanced DBS checks at the time of application but “GDPR restrictions prevent us from retaining that information”.

A spokesperson for Birmingham city council said: “Where an applicant has a previous conviction for certain offences involving violence/public order, sexual, dishonesty, serious driving or drug offences, our starting point for all convictions of this nature is to refuse the licence application.

“The onus is on them to convince the licensing authority that they are a ‘fit and proper person’ to hold a licence.”

Bradford council said it did have data on the number of people who had committed violent, drug or drink offences and were granted taxi licences, but the request would “exceed the appropriate cost limit” within a freedom of information request.

A spokesperson for Bradford council said it had implemented a suitability policy for taxi and PHV drivers and its main objective was to “protect the public and to safeguard children and vulnerable people”.

Commuters in London face another two days of disruption as a second 24-hour tube strike starts from midday on Thursday.

No further talks have taken place to settle the dispute and drivers in the RMT union will continue industrial action against London Underground plans for a voluntary four-day week after the first 24-hour strike from midday on Tuesday.

Services were reduced but not cancelled across most underground lines. Just over half of the capital’s tube drivers are members of the Aslef union, which has welcomed the four-day week plan, and were not on strike.

Early starters had to find alternative transport with services running only from 7.30am on Wednesday, as Transport for London (TfL) tried to limit overall disruption.

Wider congestion and disruption appeared far lower than in last September’s strikes by all RMT workers, with some companies in the capital relaxing rules to allow more working from home, and fine weather encouraging people to switch to cycling or walking.

Some passengers reported quieter trains than usual on lines where services operated well and commuters had not risked the tube, although most still faced long waits and crowded trains.

Santander bike hires were up 60% on Tuesday morning, TfL said, while Voi, one of the operators of e-scooter and ebike rentals in London, said rides were 52% higher than last week, with significant numbers of new users.

TfL said passengers should continue to check before travelling on Thursday, with services set to be reduced across all lines from midday and finishing by 8pm. On Friday morning the first trains will start from 7.30am.

Most of the Piccadilly, Waterloo & City and Circle lines are expected to have no service during strike hours, along with parts of the Metropolitan and Central lines. Other rail services will run, including the London Overground, Elizabeth line and the DLR.

While Aslef and TfL have expressed surprise at the strike action, the RMT said its drivers had concerns about fatigue, and blamed TfL for failing to negotiate.

TfL said its proposals for a four-day working week would bring London Underground in line with the working patterns of other train operating companies, and that drivers who wished to continue a five-day working week pattern would be able to do so.

An RMT spokesperson said the union objected to an “imposed, fake four-day week” and had raised “serious concerns from our members about shift length and resulting fatigue impacting safety”.

They added: “The strikes are going ahead because TfL said they would negotiate on all elements of the proposal and then U-turned, saying to us they would go ahead without any changes to their original proposals.

“We have sought assurances from TfL in writing that our members can stay on their current shift patterns and agreed terms and conditions. TfL have yet to respond to us adequately. So it is therefore not a voluntary scheme and TfL are seeking to impose it on our members.”

However Nick Dent, the director of customer operations for London Underground, said the “changes would be voluntary, there would be no reduction in contractual hours and those who wish to continue a five-day working week pattern would be able to do so”.

He added: “We urge the RMT to call off this strike, meet with us and avoid any further disruption to Londoners. While we have been able to run more services than planned over the last 24 hours, we expect significant disruption to continue into Friday and the level of service we can provide will vary across lines, so customers should continue to check before they travel for the remainder of this week.”

The RMT is planning four more 24-hour strikes in May and June unless the dispute is resolved.