He said last week that he wants "fair and equitable treatment" over the rezoning of his land in return for backing the Luas spur. "If I get nothing, no-one else should get anything."

Mansfield has been in talks with Harcourt Development Group's Pat Doherty and Brendan Hickey of Davy Hickey Properties, developer of the Citywest campus, on a proposal to back the Luas spur to the tune of 13m apiece.

The Railway Procurement Agency has reached heads of agreement with Davy Hickey and Harcourt over the development of the spur, but Mansfield is not on board the project.

He has applied for a variation of the draft development plan to get residential rezoning for 46 acres he owns at Citywest, and said South Dublin County Council's agreement to initiate a variation will be a condition of his backing.

The council already agreed to initiate a variation of the plan for greenbelt land at Citywest owned by Harcourt's Pat Doherty, which would enable residential development on that land.

"Pat Doherty has 70 acres of land and the council agreed to initiate a variation of the draft development plan to get zoning, " Mansfield said. "Built out, that would be worth 230m."

He noted that Hickey got land rezoned in the 2004 plan. "He has a shopping village down the road with 400 living units. The Luas will lift that considerably. He has 200 acres to develop."

Mansfield has had multiple clashes with planning authorities, the most notorious being over his project to build a 6,000-seat convention centre. "We employ about 1,000 people, and we have never been able to get anything worthwhile, " he complained, adding that he had "no fine or conviction of any sort" for planning offenses.

The public consultation process on the 3km extension of the Luas to Citywest's Fortunestown Lane is due to begin within weeks. When that process is complete, the RPA will apply for a railway order and the construction period is expected to be two and half years. It is expected that the spur could be operational by 2009.