IT will be a criminal offence for politicians to lobby Nama if one of a range of measures being proposed by the Green party is adopted by government.

The junior coalition partner wants to ensure that the proposed asset management agency does "not become a political football" and is pushing to restrict lobbying in the same way as currently happens at the decision-making stage of An Bord Pleanála and the Environmental Protection Agency. The legal basis for such a ban is being worked out with the Attorney-General.

The Greens are also seeking assurances that there will be:

* An accompanying windfall tax on property developers;

* Measures to force banks to lend to small businesses;

* A risk-sharing mechanism that will see funding being released to the banks on a staggered basis;

* Agreement that the new planning bill will incorporate measures allowing land banks taken over by Nama to be developed in a co-ordinated manner based on best planning practices and "to ensure social gain".

Agreement in principle has been reached on the risk-sharing mechanism, but other measures – in particular the windfall tax – could prove more difficult to secure agreement on. One senior government figure said that there had been "no hint" of this proposal before the end of last week.

However, there remains confidence that agreement can be secured between the two government parties. While sources stress the importance of "getting this done", there is an understanding that the Greens have to be seen to put its stamp on the Nama legislation.

Green minister Eamon Ryan said yesterday he envisaged amendments to the legislation right through to the final agreement on the bill.

"This isn't easy for anyone. It's nothing to rush in to. There are different views but we believe we've a real obligation to put our Green thinking into the legislation to promote sustainable development," he said, adding that there was still a lot of further work to be done "particularly on the planning side".

Alongside the crucial issue of valuation of the loans, Lenihan said it was also important to focus on how to ensure Nama becomes a "very positive agency that turns around the whole nature of planning in this country".

Meanwhile, finance minister Brian Lenihan has told the Sunday Tribune the government plans to sell much of the land Nama will amass to younger developers and builders previously locked out of the market for land.