Sir John Major criticised the previous Conservative government's Rwanda plan as inappropriate for the 21st century and “un-Conservative and un-British”.
The former Conservative prime minister expressed frustration that “society has come to see immigration as evil” and said he did not believe the policy worked as a deterrent.
As one of his first acts as prime minister, Prime Minister Keir Starmer in July repealed the controversial policy, which Conservatives believed would deter asylum seekers by returning those who entered Britain illegally to the East African country.
Mr Major said: “Are you seriously saying that somewhere deep in North Africa they actually know what the British Parliament has legislated for? I don't think so.”
He added that people who came to the UK on small boats did so because they “don't really know where to go”.
Labour announced on Monday that it would redirect funds earmarked for the previous government's Rwanda Plan to the border patrol force.
Major said of the Rwanda plan: “I thought it was un-Conservative, un-British, dare I say it, un-Christian in a secular society, unconscionable. I didn't think this was really the way to treat people.”
Speaking to the BBC's Amol Rajan, he added: “We were deporting people from this country almost 300 years ago. The trials may have been superficial, but they were felons who had at least been tried and convicted of something.”
“I don't think transportation policy, as it stands, is suitable for the 21st century.”
Mr Major, who served as prime minister from November 1990 to May 1997, said he had not yet decided which candidate he would support in the Conservative leadership race, which has five remaining candidates: Robert Jenrick, Kemi Badenoch, James Cleverley and Tom Tugendhat.
He said he wanted the Conservatives to attract “genuinely centre-right” people back into the party and said a merger between the Conservatives and Reform UK would be “fatal”.
Of the Conservative leadership candidate, he said: “I want to support someone who looks at the long-term issues, who can suggest which direction we should go and who will really bring centre-right people back into the party.”
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He added: “The only party that can legitimately appeal to the centre-right is the Conservative Party. And that's what we have to do. We have to identify where our natural support really lies and appeal to them.”
“Maybe people misjudged the last election. We lost five votes. [seats] People opposed to Reform UK are jumping the gun, and some rather reckless people are saying then we should merge with them.
“Well, that would be fatal.”
Asked whether Nigel Farage should join the Conservative party, Major said he “doesn't agree with that”, adding: “I don't think he's a Conservative and he's spent most of the last few years telling people that he hates the Conservative party and wants to destroy it. I don't think that's a very good background to have someone in the party.”
