The Dutch airline KLM has offered “sincere apologies” to a Paralympic athlete who was denied access to an onboard wheelchair during a long-haul flight so she could go to the toilet.

The cabin crew on the flight later called the police after the request from Hannah Babalola, 37, who is paraplegic and competes in track events, for the wheelchair, known as an aisle chair as it is narrow enough to be used inside a plane. They first handed her a written notice, headed: “Unacceptable conduct and final warning on behalf of the captain of this plane.”

The incident happened on 26 May, when Babalola, who competes for Nigeria and lives in Chicago, was returning home from a wheelchair-racing event in South Africa.

She had booked the KLM return flight from Chicago to Cape Town, via Amsterdam, as a wheelchair-using passenger. The outbound flight went smoothly, but as she began her return journey she was taken to the plane by wheelchair and asked by cabin crew, once she had boarded, if she would require an aisle chair during the flight. When she said she would – the flight to Amsterdam was almost 11 hours – the problems started.

In a conversation with cabin crew and the captain that she asked permission to record, which was shown to the Guardian, a crew member can be heard saying they could not accept a passenger in need of an onboard chair as it was too dangerous to use during a flight in case of turbulence and that Babalola’s two options were to go to the toilet without using the wheelchair or to “offload” from the plane.

“I needed to get home to Chicago to my family and to get to work and I couldn’t ‘offload’ from the flight,” Babalola said.

Security was called by the cabin crew but declined to take any action against Babalola. When the flight landed in Amsterdam, the crew asked the police at the airport to be on standby, but they too declined to take action.

Babalola transferred to a different connecting flight in Amsterdam to complete the journey to Chicago.

She said: “I felt compelled to avoid eating or drinking for the duration of the flight because I feared needing to use the restroom and being unable to access it. I spent much of the flight trying to control my emotions and I found myself crying because of the way I had been treated.

“This experience was humiliating, distressing, and degrading. The situation caused me significant physical discomfort and emotional distress. I believe that the manner in which I was treated raises serious concerns regarding discrimination and equal treatment. All passengers, regardless of disability or personal circumstances, deserve to be treated with dignity and respect.”

Babalola made a formal complaint to KLM about her experience.

A member of KLM’s customer service staff replied, stating: “It is very concerning to read about this experience, particularly the distress caused during boarding and throughout the flight. Your account describes a situation that must have felt deeply upsetting and unsettling, especially when travelling with an accessibility need and simply expecting appropriate assistance and respectful treatment.”

They added: “A full review of the circumstances should now be carried out by the appropriate teams. This will typically include examining the reports submitted by the crew and any other relevant information available in relation to the flight. My sincere apologies are extended for the distress and upset this experience has caused.”

The British Paralympian Anne Wafula Strike hit the headlines in 2017 when she was forced to wet herself on a train. The incident triggered a national debate about equal access to transport for people with disabilities.

She said: “Nine years ago I was forced to wet myself on a train because there was no functioning accessible toilet. Almost a decade later, the experience of Hannah Babalola shows we still have a long way to go. It is upsetting that disabled people are having to fight the same battles over and over again just to access the rights that able-bodied passengers have.”

A KLM spokesperson told the Guardian: “We regret that an incident occurred involving one of our passengers on the flight from Cape Town to Amsterdam on 26 May. Out of respect for the privacy of both the passenger and our crew, we find it inappropriate to discuss the details of the situation.”

Ministers have earmarked more than £170m extra to help build the Lower Thames Crossing road tunnel, fuelling concerns over the “spiralling” costs of one of the UK’s largest planned infrastructure projects.

The proposed £11bn route under the Thames between Kent and Essex is already estimated to cost more each mile than the HS2 high-speed rail link from London to Birmingham. It was given the funding boost as part of a plan to spend £3.1bn of public money on the project, before a hoped-for injection of £7.5bn by a private sector firm.

The £174m of extra cash will be used to fund public works on both sides of the tunnel and will be found from existing budgets, the Department for Transport (DfT) said.

The Guardian revealed last year that the DfT had taken direct control of the Lower Thames Crossing project, forcing National Highways to relinquish its role as the main agency involved in planning and oversight.

A licence to run the new tunnel and the existing Dartford tunnel about 7 miles to the west is expected to be handed to a private consortium in 2029, offered in perpetuity and overseen by a regulator. The completion date for works is now scheduled for 2034.

The chancellor, Rachel Reeves, and the transport secretary, Heidi Alexander, are both keen to press ahead with the project, which they have said is “vital” and will ease congestion on the M25.

However, the DfT confirmed it has yet to publish an “outline business case”, which would usually be produced before officials embark on large-scale works.

Despite the lack of an initial review document, the government allocated £590m to the project in the 2025 spending review and a further £891m in last autumn’s budget. The £1.48bn total was then given a further £174m boost in a road investment strategy document published in March, taking the total to £1.66bn.

The chancellor described the £891m awarded in the autumn budget as the “the final tranche of government support to enable the private sector to take forward construction and long-term operation”.

In total, the government has spent £3.1bn on the Lower Thames Crossing, including significant funds spent on securing planning permission.

The move to allocate extra funds to the project from the broader National Highways budget has prompted criticism, with campaigners accusing the DfT of siphoning money from the roads agency to boost spending on the tunnel without telling parliament.

Rebecca Lush, roads campaigner at the Transport Action Network accused the DfT of hunting for funds to feed a tunnel project “quickly running out of control”.

She said: “At the autumn budget, the chancellor announced the ‘final tranche’ of public funds for the Lower Thames Crossing. Yet now we find out that the DfT have bunged another £174m towards this privatised road project, whilst refusing to publish the outline business case.

“The spiralling costs and secrecy have all the hallmarks of HS2, with LTC already costing more per mile than HS2. Whilst the government is nationalising the railways it is privatising our roads, demonstrating the utter incoherence in transport policy.”

A DfT spokesperson said that the road tunnel was a vital infrastructure project, adding: “We have committed £3.1bn to the Lower Thames Crossing to date, including £891m to complete the publicly funded works needed to unlock private investment.

“While no decisions have been made on how users will be charged, any tolls will be regulated by an independent regulator to keep prices fair for drivers.”

The cost of travel to and around the UK is keeping millions of tourists away and slowing economic growth, the boss of British Airways said, as he urged a rethink of aviation taxes.

The airline’s chief executive, Sean Doyle, said the UK had some of the highest aviation taxes in the world and was falling behind countries such as Japan, France and Germany in boosting its inbound tourism.

The UK would not hit ambitious targets for domestic tourism without making travel easier and more affordable, Doyle added.

Air passenger duty across most flights was raised by 15% in April, up to £8 a passenger on domestic flights, £15 for European departures, and up to £253 in premium economy seats on long-haul flights.

“What’s the biggest challenge in the country at the minute? It’s growth. And what should policy be doing? It should be unblocking growth. If you want to promote tourism and aviation … the last thing you do to encourage that expansion is put the cost of it up,” Doyle said.

The government has set a target of welcoming 50 million international visitors to the UK by 2030, up from about 40 million tourists at present.

However, Doyle warned: “Unless we address the affordability issue we’re not going to get there. If you look at France and Spain, they’ve absolutely shot past us. A big part of it is cost, if you look at the surveys. If we want to hit 50 million and want the economic benefit of that, we’re going to have to change the affordability proposition to tourists.”

He said aviation taxes on flights around and out of the country were a factor, as well as rail ticketing: “The other thing is the lack of options to travel around the UK, because of things like rail networks which are fragmented, the lack of [rail] passes – the lack of a kind of curation of tourists is a big issue.”

“We end up with tourism concentrated in places like London and Edinburgh, but the rest of the economy doesn’t get the benefit of it.

“I think air passenger duty is a part of that – for a family of five coming into the country and travelling, it’s a huge penalty compared to what you pay in Europe.” EXAMPLE OF TAX RATES HERE?

Speaking to reporters at an international airlines summit in Rio, the Iata annual meeting, Doyle also warned that the government’s backing for Heathrow’s third runway in pursuit of economic growth could backfire if the airport developed its own scheme at the cost of airlines paying higher charges and reducing their own investments.

BA and other airlines have urged the government to pursue a cheaper alternative scheme for a third runway than the current £33bn preferred option proposed by the airport.

Doyle said: “There’s an ambition on infrastructure expansion in Heathrow, but if the cost is too high, the other side of that growth, which is airlines coming in with planes and investing their capital into the sector, that may not come.”

Flights to the Iata summit were provided by Iata and Latam airline