A top Tory has said his own Government's controversial plans to ship asylum seekers to Rwanda will only have "marginal benefit".
International Development Minister Andrew Mitchell cast doubt on the effectiveness of the scheme and admitted that the "cost is a serious issue".
Ex-PM Boris Johnson unveiled the scheme last year but the first flight to Kigali was grounded in the summer after an eleventh hour legal challenge.
The policy, which has been widely condemned by human rights groups, has since been tied up in legal wrangles.
Mr Mitchell's comments are at odds with the Government, as Rishi Sunak has made it a key priority to stop people making the perilous Channel crossing in small boats.
The former International Development Secretary was reappointed as a minister last year after a decade on the back benches where he was a vocal critic of Government policy on aid and development.
Mr Mitchell was confronted by journalist Andrew Neil over his past claim that the plan was "impractical, likely to be ineffective and above all extremely expensive".
He said: "Well, I think, whether or not you support the Rwanda scheme... it's not the answer. It may be part of an answer, but it's not the answer."
Asked about his previous criticism of the cost of the plan, he said: "I've looked at the costs and I think that the cost is a serious issue.
"But following the Rishi government statement... 85% of what we were asking for from the back benches form part of his plans. And I think now we've got to stop these boats from coming across the sea."
He went on: "What I believe is if the Rwanda scheme is to have any benefit, it will not be the whole of the effort that we have to make. It will be a marginal benefit.
"What we have to do is to stop these boats and there are a series of other mechanisms which we could use to do that."
Asked if it would only be marginal, he said: "Well, I think it's worth exploring the Rwanda scheme, but I think, as I say, that it is definitely not the whole answer."
Downing Street said the policy was "an important part" of stopping the wave of small boats arriving in Britain.
The PM's spokesman said: "We've always been clear that when it comes to dealing with this challenge, which has been very long standing, there is no single lever or single policy that can solve it in one bound.
"It will be a number of solutions put together that will finally put an end to it and that's what the Government's working on, the Rwanda Partnership, which is a very important part and obviously we're looking to expand that or some of the tougher legislation we're bringing in or the expansion of the work we're doing with our French counterparts.
"All of those are important and collectively that is what will help stop the boats."
No10 said the Government is continuing to explore similar partnerships with other countries.
The High Court said last month that its ruling that the controversial scheme is lawful could be referred to the Court of Appeal.
Several campaign organisations, including Care4Calais, had applied for the right to appeal the ruling.
