By Alex Stevenson and Ian Dunt
The police may be sitting on twenty-year-old evidence revealing "a powerful paedophile network linked to parliament and to No 10", Tom Watson alleged today.
The Labour MP prompted gasps in the Commons as he made the dramatic intervention during PMQs today.
Watson, speaking under protection of parliamentary privilege, said the evidence file used to convict a man called Peter Righton contained "clear evidence of a widespread paedophile ring".
He added: "One of its members boasts of its links to a senior aide of a former prime minister, who says he could smuggle indecent images of children from abroad.
"The leads were not followed up but if the file still exists I want to ensure the Metropolitan police secure the evidence, re-examine it and investigate clear intelligence suggesting a powerful paedophile network linked to parliament and to No 10."
Righton was fined £900 after admitting importing and possessing illegal homosexual pornography in 1992. Customs officers had intercepted a book and a magazine at their Dover postal depot in April of that year, the Independent newspaper reported at the time.
David Cameron responded by saying Watson had raised "a very difficult and complex case". He added: "I'm not entirely sure which prime minister he's referring to... I want to see what the government can do to help give him the assurances that he seeks."
Many sources believed Watson's allegations were linked to a Sunday Times story published this weekend in which former Conservative minister Edwina Currie claimed Margaret Thatcher's former parliamentary private secretary, Peter Morrison, had sex with 16-year-old boys when the age of consent was 21.
But the phone-hacking campaigner used a blog post this afternoon to specifically rule Morrison out. The Labour MP said his information came from a former child protection specialist who had been frustrated by his suspicions around the case for a number of years.
"He contacted me because he knew I had spoken out in the Murdoch scandal," Watson said.
"Over the years, he had lost faith in the ability of politicians to get to the truth. The last time he contacted an MP was in 1994. The MP promised to follow up the case but nothing came of it."
Watson, who has won plaudits for his unflinching assault on Rupert Murdoch's media empire, was understandably nervous before his appearance in parliament this lunchtime.
Earlier he tweeted: "Hoping to catch the Speaker's eye at #pmq's today. It's been a while. Feeling a bit anxious about it."