The UK government has agreed to pay France another £660m to curb the number of asylum seekers travelling across the Channel, including plans to fund a riot squad to “contain and disperse” people trying to board small boats.

Under a three-year deal to be signed on Thursday by the home secretary, Shabana Mahmood, 1,100 enforcement, intelligence and military officers – an increase of 40% – will be employed to track down smuggling gangs and people seeking refuge.

A 50-strong riot squad will be trained in “crowd-control tactics” and will “stop illegal migrants in their tracks”, according to the Home Office. UK cash is expected to fund batons, shields and teargas to deal with “hostile crowds and violent tactics”.

The announcement follows protracted negotiations between the two countries over how to halt unauthorised small boat journeys, and who should pick up most of the cost. The previous £478m, three-year deal collapsed on 31 March.

Organisations representing asylum seekers said plans to fund policing tactics such as riot control would mean the further brutalisation of people who have no alternative if they wish to seek refuge in the UK.

Sile Reynolds, head of asylum advocacy at the charity Freedom from Torture, said it was a “deeply alarming” escalation, adding: “Now, we will be paying for police boots and batons to be wielded indiscriminately against men, women and children on the beaches of northern France for the crime of seeking safety.

“Many of the people who will be harmed by these heavy-handed tactics have already endured state violence during their flight from persecution. Now they will face the full ferocity of the French riot police – a security body that has been criticised by the United Nations committee against torture for excessive use of force.”

Imran Hussain, the director of external affairs at the Refugee Council, said: “By focusing on policing the Channel, the government is treating the symptom not the cause. Policing alone will not prevent desperate people from turning to dangerous small boats in the first place.

“We know from our frontline services why people risk their lives to reach the UK: many already speak some English, have family here, or have cultural connections to Britain. Without safe routes to reach the UK, these men, women and children will be forced into dangerous and potentially deadly small boat crossings.”

French police have fired teargas canisters and stun grenades and used pepper spray in attempts to stop people boarding boats across the Channel. However, this is the first time the UK will fund a riot squad specifically to tackle irregular migration.

The new deal includes a baseline package of about £500m to boost enforcement action on beaches in northern France. The deal will cover:

Five new police units, including a riot squad of 50 officers who will be trained in the use of crowd control.

An additional 20 maritime officers to target and intercept small boats that pick up asylum seekers in shallow waters. In the past two months, French officials have stopped six “taxi boats”, sentencing smugglers to prison and deportation, the Home Office said.

An expansion of the 18-strong intelligence unit to 30 specialists to ramp up the arrest and prosecution of people smugglers.

Two new helicopters and a camera system to track down and intercept people smugglers and people seeking to cross to the UK.

The government has also put aside £160m “to trial new approaches”, but the Home Office did not respond to requests asking what these might be. In the first year of this arrangement, the UK will spend £50m, a statement said.

If the initial investment does not make an impact, the government will withhold the remaining £110m in years two and three, it says, billing it as the first “payment-by-results” scheme in the Channel.

Labour, which is predicted to lose councils to Nigel Farage’s Reform UK in the local elections, has come under increasing pressure from political opponents to curb irregular migration.

In a statement Keir Starmer, the prime minister, said: “Our work with the French has already stopped tens of thousands of crossings and this government has deported or returned nearly 60,000 people with no right to be here. This historic agreement means we can go further: ramping up intelligence, surveillance and boots on the ground to protect Britain’s borders.”

Mahmood said: “This landmark deal will stop illegal migrants making the perilous journey and put people smugglers behind bars.”

Earlier this month, a Sudanese man was charged over the deaths of four migrants who drowned after being swept away by strong currents while trying to cross the Channel. More than 6,000 people have arrived in the UK this year after making the journey, down 36% on the equivalent period last year.