Ian Paisley jnr lobbied then British prime minister Tony Blair on the future of the proposed new multimillion visitors' centre at the Giant's Causeway during negotiations on devolution, it was revealed last night.
The Democratic Unionist Assembly member also raised with Mr Blair the future of St Patrick's Barracks in Ballymena, the development of a spa resort with 200 homes, and a judicial review over a contested land deal in Ballee.
Traditional Unionist MEP Jim Allister claimed the discussions took place at the height of the St Andrews negotiations in October 2006, which led to the eventual restoration of powersharing at Stormont.
However, Mr Paisley last night denied the issues were used as leverage by his party to sign up to a deal during the talks.
Mr Allister, who was on the DUP talks team at St Andrews but who quit the party last March over its powersharing deal, published a letter he obtained under the Freedom of Information Act from the then Northern Ireland Office minister David Hanson to Mr Paisley confirming the prime minister was lobbied on six constituency issues during the St Andrews talks.
In the letter Mr Hanson told the DUP Assembly member: "The prime minister has considered your requests and has agreed that we should try to respond positively."
Mr Paisley has been criticised in the Assembly over his lobbying on behalf of the developer Seymour Sweeney, himself a DUP member, who was linked to a controversial private sector bid to build a new visitors' centre at the Giant's Causeway.
Last week the Audit Office was also asked to investigate a €50 million land deal in Ballee involving Mr Sweeney.
Mr Allister said he was astonished that the talks were used to raise constituency matters. "Ian Paisley jnr and the DUP leadership now owe a full, unvarnished explanation to the people, not only as to why these matters were prioritised but precisely what is involved in each," he said.
Dismissing the story as old news, however, Mr Paisley said: "It is now well known that on the margins of the St Andrews talks I took the opportunity with NIO ministers to raise a number of outstanding constituency cases . . . the DUP at no time used any of these matters as leverage in the negotiations . . ."