Michael Howard overruled advice from civil servants when he banned the Rev Sun Myung Moon from entering Britain, newly released documents show.
Rev Moon, the controversial head of the Unification Church, was refused entry by the then home secretary in 1995.
Mr Howard says he stands by the decision even though it was later ruled “unlawful” by a court.
Documents show he had been told by civil servants at the time the grounds for banning Rev Moon were “slender”.
The civil servants told Mr Howard: “At that time [in 1991] our view was that the grounds for refusing Mr Moon an entry clearance were slender.
Given the further passage of time that view is if anything strengthened.’
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But Mr Howard overruled them, arguing Rev Moon’s presence in the UK was not conducive to the public good.
He said he had “taken account of representations made by MPs and others about the undesirable activities of the Moonies here”.
Three days later the High Court ruled that Mr Howard’s decision was “unlawful by reason of procedural unfairness”.
The judge said that Mr Howard should have given Mr Moon the chance to make representations to him before the order was issued.
Mr Moon decided not to pursue his case to enter the UK in 1995. But he was allowed into the country last year for a two-day visit after the then Home Secretary Charles Clarke lifted the exclusion order.
Immigration officials warned Mr Howard that “exclusion at the personal direction of the Home Secretary is generally reserved for security cases”.
But nothing in the documents suggests they told Mr Howard he had to give Mr Moon the chance to put his case before taking the decision.
Mr Howard’s order followed articles in newspapers reflecting concern about recruitment methods used by the Unification Church.
The Home Office was clearly very aware of press coverage of the decision.
One official records “the announcement was to be made through an exclusive to the Mail on Sunday”.
Robin Marsh, spokesman for the Unification movement in the UK, said: ‘It was an injustice to keep a peace-campaigning religious leader from his flock. There was no sound reason for doing so.’
The revelations came in documents released by the Home Office to the BBC under the Freedom of Information Act.
But the home office has refused to release the legal advice issued to Mr Howard at the time.
Mr Howard told the BBC: “I thought his presence was not conducive to the public good because of the effect that his organisation had on families.
“This view was upheld by the court, which only decided against me on procedural reasons.
“I regret that the Home Office felt unable to release the legal advice that I received, although I understand their reasons for doing so.”