Any attempts to “push” migrant boats back to French waters risks potentially fatal capsizings, the Government has been warned amid calls for the UK to instead broker an agreement with France.

Ministers under pressure to act over record numbers of the perilous crossings are considering using Royal Navy and Border Force vessels to block the small boats in the English Channel.

But Labour former home secretary Jack Straw said any move modelled on Australia’s controversial “push-back” approach deployed against migrants from Indonesia could have deadly consequences.

“I don’t think that just trying to push these people back is going to work and it will only take one of these dinghies to capsize and everybody to drown, which is perfectly feasible, for their to be a hullabaloo, including in the Conservative Party, and for the policy to have to be reversed, so I wouldn’t go down that route,” he told BBC Radio 4’s Today programme.

“The crucial point here is the obvious one, is that it requires the co-operation of the French.”

Bella Sankey, director of the Detention Action human rights campaign, described the possibility of boats being forced back into French waters as “an unhinged proposal” which would be met with legal challenges.

She told the PA news agency: “It’s unlawful, it’s really dangerous and could seriously risk human life. From anyway you look at it it’s a terrible idea and I don’t think it would actually get off the ground.

“I think it’s really disingenuous and irresponsible of ministers to be even suggesting this. It’s more of the same, pretty transparent grandstanding to score political points while not actually coming up with any sensible or workable proposals to prevent the chaos from escalating.

“If they did try and go down the route of push-backs at sea, absolutely they would face legal challenges.”

Immigration minister Chris Philp said he will meet French counterparts next week to work “to stop these illegal migrants from getting in the water in the first place”.

But he also wrote in the Telegraph that “we need to intercept those who manage to leave France” and said he would encourage the French “to look hard at interceptions at sea”.

And schools minister Nick Gibb told Today that he UK will be using “boats to try and prevent people leaving” and crossing the English Channel.

“Australia does an operation they call ‘push back’ and it has been successful. It is one option we are looking at,” a Whitehall source told the Times.

A separate Home Office source did not rule out the option, telling PA: “There are a number of operational decisions under consideration.”

The department has said it is possible the Navy could be deployed to patrol people trying to make the journey, a move branded “completely potty” by one Ministry of Defence source.

“We don’t resort to deploying armed force to deal with political failings,” the source told PA.

The debate on how to act comes amid an increase in crossings, with warnings that smugglers are exploiting a “loophole” in the law of the sea which obliges vessels to rescue people once they enter waters in their jurisdiction.

Tony Smith, a former Border Force director-general, told PA that a “bilateral agreement” with France is necessary to prevent the situation continuing.

“I’m worried that we have not been able to broker any agreement with the French to stop the smuggling and without that we are not going to be able to do it,” he said.

Kent County Council leader Roger Gough said its services are facing “enormous” pressure in dealing with unaccompanied minors who are seeking asylum, with nearly 400 arriving this year, a figure already exceeding the whole of 2019. Sixty minors arrived in the first week of August, including 23 on Friday alone.

“We’ve not seen figures like that or anywhere near that since 2015 when we did have a very big crisis,” he said.

The greatest success seen in the past was brokering arrangements to tackle the situation with France, Mr Gough said when asked about the potential use of the Navy.

“That may be a way of dealing with it but I think certainly historically the best experience we’ve seen of reducing the inflows is when there’s been a successful agreement, level of shared interest, between the British and French authorities,” he said.

On Thursday, at least 235 migrants made the dangerous journey in 17 boats, setting a new single-day record.

And amid continued fine weather and calm waters on Friday, more than 130 migrants made it to the UK in 13 boats, the Home Office said.

On Saturday, the coastguard said it was responding to a “number of incidents” off the coast of Kent as more migrants tried to reach the UK.