The Traditional Unionist Voice leader said he believed the contact was known to at least one DUP negotiator and there were also suggestions a elected representative had "direct or indirect" meetings with Sinn Fein.

DUP deputy leader Peter Robinson and others have flatly denied the allegations, revived this week with the publication of extracts from a book from Tony Blair's former chief of staff, Jonathan Powell.

Another book just published, Paisley: From Demagogue to Democrat by veteran journalist Ed Maloney, claims Mr Powell refused to meet DUP delegations after December, 2004, if Mr Allister was present.

The MEP said, however: "Given Powell's pivotal role in negotiations he is in a position to know and his claims are unlikely to be lightly made. Nor does misinformation from him at this stage serve any obvious purpose.

"I must say that his assertion fits with suspicions which I, and I believe others, had when I was within the DUP. It is my suspicion that a DUP staffer and a journalist were involved in such a back channel of protracted contact with Sinn Fein and that such was known to at least one senior negotiator.

"Moreover, there were suggestions that an elected representative had meetings, direct or indirect, with Sinn Fein."

The MEP said with the renewed speculation, coming on top of Mr Moloney's " unchallenged" claim that two DUP MPs met Sinn Fein during the St Andrews negotiations "it seems to

me that a lot more clarity and transparency must attend how the DUP deals with these matters."

A DUP spokesman was not immediately available today but this week Mr Robinson insisted the first meeting with Sinn Fein involved himself, Nigel Dodds and Ian Paisley Jnr in March of last year.

Mr Powell claimed the channel was established soon after the DUP became the main unionist party in the Assembly election of 2003.

East Londonderry MP Gregory Campbell added, however: "It could well be the case that the Government played intermediary, but he (Powell) is going much further than that, he's suggesting that there was direct back-channel contact between us and Sinn Fein, which there wasn't."

Sinn Fein has said it is making no comment on the book.