Jack Straw has warned Rishi Sunak he will be left âembarrassedâ by the latest plan to tackle small boats crossing the Channel.
The former Labour home secretary said the governmentâs new plan was a âpiece of red meatâ being âchucked at the right wing of the Tory partyâ.
Straw said it was a âdesperate measureâ that would not work and ultimately leave the prime minister humiliated.
He made the comments as the government was set to unveil new laws on Tuesday to stop asylum seekers making the perilous journey across the Channel.
The new legislation will place a duty on the home secretary to remove anyone who enters the UK by an illegal route.
It will also prevent those arriving illegally from claiming asylum or returning to the UK in future.
Straw told Sky News: âThey keep coming up with these desperate measures.
âThis latest measure - which is to try and override all these international obligations and turn ourselves into a kind of pariah amongst western European states - is not going to work anyway.
âI promise you, in a year to 18 months time when thereâs a general election Mr Sunak will be very, very embarrassed about the fact that the numbers may have come down a bit, but they have not stopped.â
Asked how banning an asylum seeker for life could work, Straw replied: âI donât know. This sounds like stuff written on the back of an envelope for the benefit of - red meat if you like - being chucked at the right wing of the Tory party, without really thinking it through.â
Home secretary Suella Braverman said the bill would push âthe boundaries of international lawâ, telling the Express this was needed to âsolve this crisisâ.
Labour leader Sir Keir Starmer has described the plans as âunworkableâ and the Lib Dems slammed them as âimmoral, ineffective and costlyâ.
The plans have been likened to the failed Rwanda scheme - a controversial policy unveiled in April last year, with former prime minister Boris Johnson saying action was needed to stop âvile people smugglersâ.
However, no-one has been sent to the African country and thousands have continued to cross the worldâs busiest shipping lane in precarious dinghies.
The High Court has ruled that the governmentâs policy of deporting asylum seekers to Rwanda is lawful.
However, even Tory ministers have admitted the policy would only have âmarginal benefitâ in stopping asylum seekers crossing the Channel.
The latest Home Office figures show 2,950 migrants have crossed the Channel already this year.
Writing in The Sun, Sunak said the plans were âfair for those at home and those who have a legitimate claim to asylumâ.
A Home Office spokesperson said: âThe home secretary has been clear that if you arrive in the UK illegally, you should not be allowed to stay.
âWe will shortly introduce legislation which will ensure that people arriving in the UK illegally are detained and promptly returned to their home country or a safe third country.
âOur work with France is also vital to tackling the unacceptable rise in dangerous Channel crossings. We share a determination to tackle this issue together, head-on, to stop the boats.â