Mr Kerr, who was sent to Kincora in 1975 when he was 14, also said he was trafficked from Belfast to London and taken to the Dolphin Square flats in Pimlico, where children are alleged to have been abused by well-connected paedophiles in the 1980s.

In 1981, three senior staff at Kincora - Joseph Mains, Raymond Semple and William McGrath - were jailed for abusing 11 boys. Mr Kerr told Channel 4 News " two plainclothes policemen" visited him before the trial.

Interrogated

He said: "They came to my home and they removed stuff from my drawers, and they put me in a car and they took me to the police station and they interrogated me, put me in a cell for seven hours and as they removed me from my cell, they made it clear to me that I'm not to talk about this and that I'm lying and not to tell lies, and I felt they were giving me a warning."

I think this person smoked cigars. Those were the things I do remember

Mr Kerr said he was being warned about the forthcoming Kincora case. "The case was coming up... and they didn't want me to come to the trial".

He added: "First of all, they intimidated me by bringing me to a station and putting me in a cell. They wanted to make it clear that I'm not to say anything. They also said to me that if you tell any lies, if you talk about this, that we can put you away. So at that moment I stopped wanting to volunteer what my experience was in Kincora."

Trafficked

Mr Kerr said he was trafficked to London and taken to Dolphin Square. "I was picked up at a Wimpy bar off Piccadilly Circus. Upstairs at the Wimpy bar, this is where they were making arrangements for boys to be picked up.

"I was with someone, well dressed. I remember entering that place (Dolphin Square). Very nice furniture. I remember being offered a brandy actually in a Waterford crystal glass. I think this person smoked cigars. Those were the things I do remember."

Asked who had met there, he said they were "very well off, very well established".

There have been allegations that abuse at Kincora, which closed in 1980, was covered up, with the collusion of the intelligence agencies.

What happened there is currently being investigated by Northern Ireland's historical institutional abuse inquiry, but there is pressure for Kincora to be considered by the wider judge-led inquiry set up by Home Secretary Theresa May.