The politician implicated in an alleged child sex ring at 10 Downing Street was Sir Peter Morrison, one of Margaret Thatcher's closest advisers, IBTimes UK can reveal.

Morrison was the mystery "senior aide" MP Tom Watson alluded to at Prime Minister's Questions (PMQs). Watson's allegation of a paedophile ring close to Downing Street stunned the House of Commons.

Morrison was a Conservative politician who acted as Thatcher's parliamentary private secretary while she was prime minister. He also masterminded her failed bid to hold on to the leadership in 1990.

Morrison left office in 1992 and died in 1995.

The sexual tastes of the prime minister's trusted adviser were an open secret in some quarters but were concealed by a police cover-up and threats of libel by Morrison himself, according to a former editor of the Sunday Mirror, Peter Connew.

Simon Heffer wrote in the Daily Telegraph in 2009: "At least one member of Mrs Thatcher's first cabinet was homosexual. Her last parliamentary private secretary, Sir Peter Morrison, was a constant trial to the whips, who were afraid that his late-night cruises around and skirmishes in Sussex Gardens would come to the attention of the press."

Connew told IBTimes UK that he saw first-hand how efforts to name and shame Morrison were hampered.

Morrison, the MP for Chester, was arrested more than once for pestering young boys in public toilets for sex, said Connew. When police officers tried to charge him, the cover-up began.

"Such was the hush-up that nobody could get hold of the log of the arrest," Connew told IBTimes UK.

"As soon as he was brought in for importuning young boys in public toilets, the seniors would come down. That was the reason the officers leaked the details: they were outraged that the seniors had ticked them off for arresting him.

"If they had nicked a lorry driver, he would have been up before the judge in no time."

Print and I'll sue you

When reporters acting on tip-offs doorstepped Morrison, he came out fighting, added Connew.

"When they doorstepped him, he said 'print and I'll sue you.' This is something that Lord Leveson might want to consider."

Allegations against Morrison first surfaced in the press in 1998. Investigative journalist Nick Davies reported how Chris House, crime editor at the Mirror, had been tipped off by police about Morrison's activities - but was gagged by legal fears.

Not being able to expose the politician close to No 10 irked House, said Connew. "He categorised it as the most frustrating scoop he could never write. He was more involved in it than me.

"I had no idea Tom Watson was going to set off that hand grenade in parliament," he added.

Morrison's activities were thrown under the spotlight by Labour MP Watson at PMQs. The West Bromwich East MP alluded to a political figure who was cited in evidence at the 1992 trial of paedophile Peter Righton, real name Paul Pelham.

Watson said in parliament: "The evidence file used to convict paedophile Peter Righton, if it still exists, contains clear intelligence of a paedophile ring.

"One of its members boasts of his links to a senior aide of a former prime minister who could smuggle indecent images of children from abroad.

"The leads were not followed up but if the file still exists I want to ensure that the Metropolitan Police secure the evidence, re-examine it and investigate clear links of a powerful paedophile network linked to parliament and No 10."

Righton was a high-profile public expert on the UK childcare system. He was convicted of importing and possessing child pornography in 1992.

UPDATE (25 OCTOBER 2012) Watson has gone on record to deny that the mystery aide referred to in his statement at PMQs was Peter Morrison, former aide to Margaret Thatcher when she was in power. Morrison was recently named by former Tory MP Edwina Currie as having had sex with teenage boys.