More than 170 migrants have been rescued after the boat they were using to cross the Channel caught fire on Tuesday morning, as the UK government said “all will be returned” to France.

The boat was attempting to cross to the UK when its engine caught fire, according to the French maritime prefecture of the Channel and North Sea.

It had originally reported 157 migrants were rescued, but has since revised that figure up to 173. All have been taken to Boulogne-sur-Mer in France, with 11 people suffering from minor injuries.

French prosecutors have opened an investigation, and an Egyptian national has been taken into policy custody in connection with the incident.

Border Security Minister Anna Turley said the incident “shows the dangers of these illegal crossings and the ruthless gangs behind them”.

“That’s why we are bearing down on them,” she said.

French authorities said the boat left France on Monday night.

Overnight “five people on board the vessel required rescue… the remaining people on board refused the assistance offered by the French patrol boats”, the French maritime prefecture said.

“Determined to reach the United Kingdom, migrants crossing the Channel in small boats refused assistance offered by French emergency service, accepting it only in situations of extreme emergency,” it said in a statement.

Because of the “structural fragility” of boats used to cross the Channel, it said they decided not to intervene further at that stage.

But this morning the engine caught fire and the “vessel’s integrity deteriorated very rapidly”.

Rescue boats went to the scene from France and the UK, including the RNLI Eastbourne lifeboat and the UK Border Force vessels BSC Contender and BSC Courageous.

The French maritime prefecture said the operation involved 40 firefighters, 13 police officers, seven interpreters, and a number of medical personnel.

It had previously reported that 157 migrants were rescued, but on Tuesday afternoon revised that figure up to 173.

On top of the initial five rescued, two French boats rescued 105 migrants and the British boats rescued 63. All of them were taken to Boulogne-sur-Mer for treatment.

A UK government spokesperson said the Border Security Command was alerted to an incident in the Channel this morning “concerning a migrant small boat in distress in French waters”.

It said British vessels assisted in the operation, adding that so far there have been no fatalities reported.

They added that the incident “underlines the terrible dangers of small boat crossings”.

“We continue to work relentlessly with the French and our partners overseas to prevent these perilous journeys,” they said.

Shadow home secretary Chris Philp said: “This is why it’s so wrong that French police stand by and do nothing while the illegal migrant boats embark – lives are being risked.”

Reform UK leader Nigel Farage said in a post on X: “We must put a stop to this. Our plan will save lives.”

Earlier this week, his party said if in government it would deploy the navy to ward off crossings.

Political discussions around the UK’s policies on illegal migration have resurfaced since tens of thousands of migrants swam into the Spanish exclave of Ceuta on Thursday.

The Conservatives have said that Labour has not delivered on its promises on migration, while the Lib Dems said the government should increase efforts to improve relationships with Europe and cut down the asylum backlog.

The number of migrants who have arrived in the UK on small boats since Burnham became prime minister a fortnight ago surpassed 2,000 on Saturday.

Last Wednesday was the busiest day for crossings so far this year, with 752 migrants arriving in the UK.

Most people attempt the crossing in the summer when conditions are better. It’s also become the most common way for people to be detected entering the UK illegally.

Home Office figures show the number of crossings so far this year are down about 43% compared to this time last year. The number peaked in 2022 and has been on a downward trend ever since.

During a visit to Dover on Monday, Prime Minister Burnham pledged his government will be “relentless” in curbing the number of people arriving in the UK on small boats.

He said progress had been made in curbing the number of people arriving in the UK on small boats, adding that “people want to see this issue addressed”.

Burnham said enforcement officers tackling people-smuggling gangs have been doubled on both sides of the Channel, but “a system that offers safe routes for people” needs to be built as well.

In April, the UK and France struck a £662m (773m euro) deal aiming to stop illegal migrants from crossing the Channel.

The three-year agreement included plans to send riot-trained police to French beaches to tackle violence and “hostile crowds”, as well as France deploying millions of pounds of drones and two helicopters as part of a system to intercept people smugglers and illegal migrants.

UK ministers have also said about £100m in funding could be redirected or withdrawn after a year if not enough journeys are stopped – but the government has not confirmed what targets the French would have to meet.