* McAlpine denies 'false and seriously defamatory' claims
* PM Cameron warns of witch-hunt against gays
* BBC aired paedophile claim against Conservative
* Abuse scandal stokes fears of high-level ring in Britain
By Guy Faulconbridge and Michael Holden
LONDON, Nov 9 (Reuters) - The treasurer of the Conservative Party under former Prime Minister Margaret Thatcher denied on Friday allegations he had sexually abused children in the 1970s, casting doubt on a BBC report that stoked fears of an elite British paedophile ring.
Lord Alistair McAlpine, a Thatcher ally who served as Conservative treasurer from 1975 to 1990, said ill-informed commentators had wrongly named him in a "media frenzy" as the mystery paedophile accused by one victim in a BBC report on the rape of children in social care.
From the BBC to the police and the National Health Service, some of Britain's most venerated institutions have grappled with claims they failed to protect children from Jimmy Savile, a former BBC presenter who was unveiled as a prolific child sex offender in October.
A Nov. 2 BBC report about child abuse by an unidentified Conservative Party figure and claims by a lawmaker about a high-level paedophile ring with links to a former prime minister's aide, propelled the scandal firmly into the political sphere as well.
Prime Minister David Cameron commissioned an investigation after the BBC report and a host of Conservative Party figures - including McAlpine - were named on Internet and social media sites as paedophiles whose alleged crimes had been covered up.
"Even though these allegations made of me by implication in the broadcast and print media, and made directly about me on the Internet, are wholly false and seriously defamatory, I can no longer expect the broadcast and print media to maintain their policy of defaming me only by innuendo," McAlpine said.
Lord McAlpine, who said he was in poor health, warned he may sue to protect his reputation but said he had sympathy for the plight of Steven Messham, the child abuse victim quoted by the BBC as naming a leading Conservative Party figure as his rapist.
"I am, as is now well known to readers of the Internet and to journalists working for the print and broadcast media, one of the individuals implicated by Mr Messham," McAlpine said.
At least 10 inquiries have been been ordered amid allegations of cover-ups at the BBC, the police and at senior levels of public life, including one into widescale assaults at children's care homes in North Wales where Messham was abused.
A major police investigation is also under way, looking into claims made by hundreds of victims that Savile and accomplices abused them. Detectives have questioned former glam rock singer Gary Glitter and comedian Freddie Starr.
Both men have been released on bail.
McAlpine said he had only once been to Wrexham, the town in north Wales where Messham's care home was located, and had always been accompanied during his visit.
"I have never been to the children's home in Wrexham," McAlpine said. "I did not sexually abuse Mr Messham or any other residents of the children's home in Wrexham."
Messham, who said he was abused "more than a dozen times" by the Conservative figure, did not answer the door at his home on Friday. Written requests for comment were left unanswered.
"I do not suggest that Mr Messham is malicious in making the allegations of sexual abuse about me," McAlpine said. "If he does think I am the man who abused him all those years ago I can only suggest that he is mistaken and that he has identified the wrong person."
Allegations linking the scandal to the Conservatives could be damaging to Cameron's party - which rules in an uneasy coalition with centrists - and tarnish the image of the era of Margaret Thatcher, prime minister from 1979 to 1990.
Cameron has warned that speculation about the identity of alleged abusers could become a "witch-hunt" of homosexuals.
"I have heard all sorts of names bandied around and what then tends to happen is, of course, that everyone then sits around and speculates about people, some of whom are alive, some of whom are dead," Cameron said during an interview on Thursday.
During the ITV television interview, Cameron was passed a piece of paper with the names of people identified on the Internet as being alleged child abusers. Some of the names were visible to viewers.
"There is a danger, if we are not careful, that this could turn into a sort of witch-hunt, particularly against people who are gay," Cameron said.