The BBC has "unreservedly" apologised for broadcasting child sex abuse allegations which led to a former Tory party treasurer being wrongly accused.

The corporation issued its statement after abuse victim Steve Messham admitted that the man who abused him in the 1970s and 1980s was not Lord McAlpine.

The 70-year-old peer found himself at the centre of a storm of internet speculation after Mr Messham told BBC2's Newsnight that he had been abused by a senior Conservative from the Thatcher era when he was a teenager at a north Wales children's home.

In a statement issued this evening, the BBC said of its November 2 Newsnight programme: "We broadcast Mr Messham's claim but did not identify the individual concerned. Mr Messham has tonight made a statement that makes clear he wrongly identified his abuser and has apologised. We also apologise unreservedly for having broadcast this report."

The BBC said director general George Entwistle designated a senior news executive to supervise Friday's edition of Newsnight, which carried a full apology.

BBC Scotland director Ken MacQuarrie will write an urgent report for Mr Entwistle covering what happened on the programme's investigation into the north Wales children's home scandal.

In the meantime there will be an immediate pause in all Newsnight investigations to assess editorial robustness and supervision.

The BBC is also suspending all co-productions with the Bureau of Investigative Journalism which worked with Newsnight on the investigation.

In a statement quoted by the BBC, Mr Messham said: "After seeing a picture in the past hour of the individual concerned, this is not the person I identified by photograph presented to me by the police in the early 1990s, who told me the man in the photograph was Lord McAlpine. I want to offer my sincere and humble apologies to him and his family."

Earlier, Lord McAlpine broke cover to issue a vehement public denial of the "wholly false and seriously defamatory" claims against him. Representatives for the peer said solicitors were preparing writs with a view to taking legal action against "all media who have defamed Lord McAlpine's reputation and published defamatory statements".