The UK’s migrant return deal appeared to be a laughing stock on day one as French authorities continued to run a “taxi service” for dinghies crossing the Channel. Sir Keir Starmer’s plan to smash the gangs faced ridicule after the Daily Express – alongside Shadow Home Secretary Chris Philp – witnessed two boats carrying dozens of people being shadowed within 30 minutes of each other. After escorting one of the dinghies to British waters, the French navy vessel’s captain then contacted a Border Force boat over the radio to ask for its 60 lifejackets back.

In a stark assessment, Mr Philp said: “The people-smuggling conveyor belt is now a round trip, paid for by British taxpayers. We were in the middle of the Channel, just on the UK side of the border, witnessing the French handing over two boatloads of illegal migrants, Border Force picking them out, providing a taxi service back to the UK. This is the first day of the Labour Government’s new plan and here is evidence it is not working at all. I mean, even seeing the French asking for their lifejackets back so they can facilitate even more illegal immigration later on. With a weak Government in the UK, the [French] are essentially assisting and facilitating illegal migration [so it’s] no wonder we’ve got the worst ever numbers.”

Sir Keir – amid political criticism of his deal – insisted the “one-in, one-out” pact struck with Emmanuel Macron is a “deterrent” and sends a “very strong message” to migrants and smugglers.

Border Security Minister Dame Angela Eagle said it would “take time” to have an impact during an extraordinary row with Mr Philp.

But the Shadow Home Secretary told the Daily Express: “Labour ministers are scrambling to defend a deal they clearly haven’t even read. Dame Angela Eagle might think the treaty is watertight, but the truth is it is littered with loopholes. The meaning of Article 4 is clear in black and white.

“If the Home Office are now denying it, they either don’t understand what they have written or have simply made a foolish mistake. There are no [return] numbers specified, presumably because they are so small they would embarrass the Home Secretary.

“France won’t even tell us any information about who we have to accept back, so they could be criminals or terrorists, and we wouldn’t know.

“I saw it with my own eyes – French warships escorting dinghies in the Channel on the very day Labour’s big new deal was meant to come into effect. You couldn’t make it up.”

Mr Philp challenged the Prime Minister and Home Secretary Yvette Cooper to watch the crisis in the Channel unfold from the water.

Former Border Force chief Tony Smith said: “The reason Rwanda never got off the ground was because of unrelenting opposition and delay by Labour in the Commons and the Lords. Constant legal challenges by human rights lawyers both in the UK and ECHR. That would have been a much better deterrent than this deal.”

The new treaty enforcing the “one-in, one-out” deal between London and Paris came into force on Tuesday. It will see illegal migrants arriving by small boats to the UK being returned to France, in exchange for Britain accepting an equal number of legitimate asylum seekers with UK family connections.

However, under the agreement, France will be able to hide crucial details about the asylum seekers they are sending to the UK. Mr Macron’s country can also refuse to take any Channel migrant that poses a “threat to public policy, internal security, public health or the international relations of any of the Schengen States”, according to the treaty’s Article 4.

And small boat arrivals with “clearly unfounded” human rights claims will be allowed to stay in the UK until they have exhausted all their legal challenges.

Fresh confusion erupted after Culture Secretary Lisa Nandy claimed migrants sent back across the Channel could have their human rights claims heard in France, despite the text of the treaty stating otherwise.

Britain will also pay for the transportation costs of every migrant transferred to and from France.

Shadow Foreign Secretary Dame Priti Patel said: “Labour’s never-ending cover-up on illegal migration continues.

“Behind the spin, let’s look at the facts and how dangerous migrants will be dumped in Britain.

“Under Article 4 of the Treaty, the UK cannot send back to France any individual considered to be a pre-existing threat to ‘public order or national security’ of the UK (para 2.b).

“And France ‘shall refuse’ to take back anyone they deem to be a threat to them and other Schengen States, or where there is an alert registered against that individual.

“This means dangerous people who have crossed illegally from France to the UK are not covered by this scheme.

“If they are deemed to be a threat to the UK, to France or a country in the Schengen area, they all become our problem.

“There’s no incentive for the French authorities to stop those who pose a threat or danger from crossing to the UK.

“In fact, it’s in French interests for them to make it to the UK. Labour is failing to keep us safe.

“But we should not be surprised. Labour opposed the Rwanda deterrent, voted against life sentences for people smugglers, and campaigned to block the deportations of dangerous foreign national offenders.

“Labour is a toxic Government working against our national interests.”

But Sir Keir told Channel 5: “Successive governments have tried to get a scheme like this off the ground. We’ve built good relations with France and we’ve got the scheme up and running.

“The most important thing is that it’s a deterrent because it says to people if you make that journey by boat you may well be returned to France, back to where you started. That is hugely important, obviously.

“It’s a pilot at the moment. We need to see how it works.

“But I’m really pleased that we’ve struck this deal. I think it will send a very strong message and we can build on this as we go forward.

“But there’s a reason why successive governments have been trying to get this to work and that’s because it could be very effective and I’m really pleased that we’ve done the hard yards, the serious work with the French government.

“Previous governments were in a shouting match with the French, they didn’t get these sorts of agreements over the line. We’ve approached it in a sensible, grown up, serious way.

“Now let’s get it to work.”

Border Security Minister Dame Angela defended the deal and accused Shadow Home Secretary Mr Philp of being “desperate for this pilot to fail”.

In a bitter row over the Rwanda deportation scheme, Ms Eagle told the Shadow Home Secretary: “The fact is that 84,000 people and 1,835 boats crossed the Channel from the day the Rwanda treaty was signed to the day it was scrapped.

“You never succeeded in deporting a single person under the terms of the treaty.

“We’ve learned the lessons from that failure and we’re determined to make this returns scheme deliver actual results.

“It will take time, and it will be hard, but as we get it up and running it will make an important contribution to the all-out assault we are waging against the business model of the smuggling gangs, which was allowed to flourish and grow for six years while your Government was in charge.”