The claim coincides with a fresh initiative, by lawyers representing Hanratty's family, calling on the Home Office to reopen the case.
Hanratty, who protested his innocence to the end, was executed in April 1962 for the murder of Michael Gregsten in a lay-by on the A6 the previous August. Gregsten's girlfriend, Valerie Storie, was raped, shot and left for dead at the same time.
A book by Paul Foot, Who Killed Hanratty?, produced witnesses in 1971 who maintained that Hanratty was in Rhyl, north Wales, on the night of the shootings. In April this year, in Hanratty: Mystery of Dead Man's Hill, a documentary for Yorkshire TV, the film-maker Bob Woffinden called for DNA tests to be carried out to establish the true identity of the murderer.
Now, to the dismay of the pro- Hanratty lobby, a former RAF police corporal has come forward with an account of a conversation he says he had with Hanratty at RAF Halton near Wendover, Buckinghamshire, in late 1961.
John Needham, now 65 and a security guard at a country club outside Bath, says he was duty NCO in the guardroom on the night Hanratty was brought in to attend an identity parade.
'We stood in the rear of the guardroom and I asked him if he'd like a cigarette and a cup of coffee,' he said. 'We were just chatting. I asked him what he thought his chances were and he replied, 'They know I did it. I know I did it, but I don't think they can prove it. It's not up to me to help them'.
'After 30 years I can't remember anything else about the conversation except that it was very brief.
'He was quite openly cocky about it, very bumptious. I think he looked on it at the time as a bit of a game he was playing.'
Mr Needham gives a number of reasons for not revealing the conversation at the time - including distrust of the civilian police, forged by his own experience as a constable with the Wiltshire force, and preoccupation at the time with personal problems involving the break-up of his marriage.
He says he decided to go public when he saw a newspaper article complaining about miscarriages of justices and citing as an example the Hanratty case. 'I thought: 'God, is this never going to stop?' They all seemed to be talking from their own personal point of view, flogging it to death and I thought: 'At least I spoke to the man'.'
Mr Foot dismisses Mr Needham's evidence as absolute nonsense. 'There's no conceivable way Hanratty could have incriminated himself in this way,' he said. 'There's not one single example anywhere of him saying he'd had anything to do with the killing. We've 14 witnesses, including whole numbers of people who were not at the trial, who showed that Hanratty was in Rhyl.'
Geoffrey Bindman, the solicitor representing Hanratty's mother and brother in the latest call for a judicial review, is equally dismissive. 'It's hard to understand why it's not already been accepted that Hanratty was not the murderer,' he said. 'The evidence against him was so full of holes. Frankly, the subsequent inquiry in 1975 was quite unsatisfactory.'
He said Mr Needham's story contained many absurdities, and he regretted that the Independent was giving it publicity.
A Home Office spokeswoman said: 'We understand the Hanratty solicitors are going to make a further case, perhaps for a judicial review, and obviously we're prepared to consider that.'
Mr Bindman said he would make his submission within two months.
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