The letter is dated September 10 and has been stamped by the minister's Private Office as having been "received" on that date.

Mrs Foster's department has stated that she did not personally see the correspondence before making her September 10 announcement that she was minded to approve the developer's Causeway scheme.

In the four-page letter, Mr Sweeney's solicitors detailed the five-year history of his planning application for a new visitors' centre and argued for a prompt decision to be made.

It referred to case law, while contending that the minister has the authority to overrule advisers on developments - including those affecting World Heritage sites like the Causeway.

The Environment and Heritage Service of the Minister's Department has recommended a planning rejection for the proposed visitor centre.

The September 10 letter was sent three days after the developer had won a landmark legal victory over the department.

In that case, the High Court had upheld his judicial review challenge against the Northern Area Plan, a development framework covering the north coast.

The September 10 letter on the Causeway visitor centre application was presumably faxed, given the date of the "received" stamp.

Mrs Foster's "minded" announcement on that day triggered a major political controversy that is still raging two months later.

A DoE spokesperson yesterday said: "The minister did not have sight of the correspondence from Carson McDowell Solicitors dated September 10, 2007 prior to making her announcement."

A spokesperson for Mr Sweeney's firm Seaport said the letter had been drafted some time earlier.

"It was issued after we were notified by the minister's office that an announcement was going to be made," the spokesperson added.

The minister has stated that a final decision on the controversial visitor centre application will be taken after DoE Planning Service has consulted with Seaport and two key stakeholders at the Causeway - Moyle District Council and the National Trust.

Meanwhile, the DoE has confirmed that it "conveyed" an offer to Moyle Council from Mr Sweeney at a meeting this week.

Planning Service chief executive David Ferguson has written to the council to "set out the proposal that I conveyed on behalf of the developer" .

According to his letter, the offer involves the council removing its existing visitors' centre and car park in return for a compensation package from Mr Sweeney.

Sinn Fein MLA Daithi McKay has accused Planning Service of acting as a go-between for the developer.

On Tuesday, the Minister dismissed his claims of "irregular behaviour" as "utter rubbish" and accused him of "petty party political point scoring".

Planning Service said it is "in no way trying to negotiate or act on behalf of any one party". It also stated that Moyle Council was refusing to meet directly with Mr Sweeney.

In a statement, Seaport said it was charged with maintaining confidentiality on the consultation process.

"We would not wish in any way to breach that undertaking," it added.