Labour's 'one-in, one-out' policy was plunged into chaos on Tuesday night as the High Court blocked ministers from sending a small-boat migrant back to France.

The ruling – the first challenge to the policy to reach court – is likely to pave the way for others at risk of deportation to bring copycat claims.

It could leave Labour's returns deal in legal limbo for months. The dramatic court ruling came after attempts to deport other migrants aboard two flights from Heathrow airport were blocked by separate last-minute legal actions.

Shadow Home Secretary Chris Philp, who predicted in Monday's Daily Mail that Labour's scheme would face a 'slew of legal challenges', said the plan was now 'clearly dead'.

'The Government's latest Channel migrant gimmick is now in complete disarray,' the Tory frontbencher said.

'Two flights, a legal defeat in court and zero deportations. Not a single migrant has been removed, yet thousands more continue to arrive.

'This plan is clearly dead. Vexatious human rights and modern slavery claims have ended it before it even started.'

Prime Minister Sir Keir Starmer – who scrapped the Conservatives' Rwanda asylum deal as one of his first acts in office – previously claimed that his agreement with French president Emmanuel Macron would see migrants 'returned to France in short order'. 

 Labour was repeatedly warned that the European Convention on Human Rights (ECHR), which is enshrined in domestic law by Labour's Human Rights Act, would prove to be a massive stumbling block to its proposals.

However, the Prime Minister has insisted that Britain will never leave the human rights treaty.

Before he entered politics, barrister Sir Keir edited a legal manual on how to interpret the new human rights laws shortly after they came into force, describing how they had 'enormous potential' and represented a 'new way of thinking' about the law.

Tuesday's High Court case was brought by an Eritrean migrant who arrived in Britain only five weeks ago.

He claims he will be 'destitute' if the Home Office sends him back to France, breaching his human rights.

The 25-year-old man, who was granted anonymity by the court, had been due to be placed aboard an Air France flight to Paris at 9am today.

His legal challenge argued that his deportation would risk multiple human rights breaches. 

The migrant told the Home Office he and his mother travelled to Ethiopia when he was a young child, and that he was trafficked from there to Libya in 2023.

The man then made his way via Italy to France and arrived in Britain by small boat across the Channel on August 12 after his mother paid £1,000 to smugglers.

The following day during an asylum screening interview with the Home Office, he was asked if he had been exploited and replied 'no', court papers showed.

But a few days later he lodged a claim under British modern slavery laws alleging he had been exploited in Libya. 

His barrister Sonali Naik KC, a former chairman of human rights group Liberty, told the court there was 'a serious issue to be tried' about whether the man, who alleges he has a gunshot wound in his leg, would face destitution.

She referred to a Strasbourg case from 2020 which ordered the French government to pay compensation to five asylum seekers after they were denied support and forced to sleep rough.

In that case they claimed they had been subjected to 'inhuman and degrading conditions' in breach of Article 3 of the ECHR.

As a result, Ms Naik said 'there is evidence that simply being a signatory [to the treaty] is not going to be sufficient' to prevent her client suffering destitution.

However, it was the migrant's modern slavery claim which proved crucial in persuading the High Court to temporarily block his removal.

The emergency hearing – which went on until after 7pm on Tuesday – was told the organisation which examines the claims would not be able to carry out its work if the applicant was abroad.

Mr Justice Sheldon said he was granting an interim injunction which would bar the Home Office from deporting the man for 14 days.

The judge said: 'It seems to me there is a serious issue to be tried with respect to the trafficking claim and whether or not the Secretary of State [Shabana Mahmood] has carried out her investigatory duties in a lawful manner.' 

The court case came after an attempt to remove one migrant aboard an Air France flight from Heathrow to Paris' Charles de Gaulle airport was abandoned on Monday, followed by another yesterday.

It is thought lawyers for the migrants similarly submitted late legal challenges shortly before the removals were due to take place.

The PM's official spokesman denied that the blocking of the first two flights meant the system was 'a shambles' or that ministers were powerless against the courts.

'France is a safe country and we are expecting the first flight to take off imminently,' he told reporters. A Home Office spokesman supported that statement.

Since the 'one-in, one-out' deal came into force on August 7, more than 5,400 small-boat migrants have reached Britain.

The delays – and the prospect of more challenges ending up in court – are a massive blow for the Government as it comes under intense pressure to tackle the Channel crisis.

So far this year, 31,026 migrants have arrived – up 38 per cent on the same period last year.

Former home secretary Yvette Cooper was moved sideways to the Foreign Office in this month's reshuffle after she failed to make progress.

The Home Office refused to discuss details of the returns scheme.