Development property experts are broadly in agreement with John Mulcahy, Nama's property adviser, that commercial property values recover from the bottom of the market usually in seven-year cycles, based on evidence since 1971.

However the caveat they add is the standard financial advice that "past performance is no guarantee of future returns" and nobody has ever seen anything like this before.

"Values tend to push forward, then back," said one expert. "Land values are up and down hugely over time."

Much of Nama's future will depend on those land prices, which are generally accepted to have fallen 70% from their peak, with Friends First' economist Jim Power suggesting some land is down 95% in value and is of agricultural value only. Appearing before an Oireachtas committee recently, Mulcahy agreed broadly with the idea that some of the land is of use only to farmers.

"I agree there is an issue in regard to the fabled land banks on the outskirts of towns. There are many rural towns where the amount of land available for development seems to exceed dramatically any potential demand in the foreseeable future," he said. "The fact that a parcel of land might be ripe for development in 20 years' time does not mean it is worth much today. I expect much of this land to revert to agricultural value; that is what we will pay for it. Unless there is a long-term economic value that can be described, articulated and mathematically proved, there is no way we can assign a greater value to it."

UCD professor Morgan Kelly was the first economist to correctly predict that house prices would fall between 40% and 60% from their peak. He based his forecast on an analysis of almost 40 house price booms and crashes that have occurred in OECD economies since 1970. Kelly, however, thought it could happen over eight or nine years; in fact it has happened in less than three. Property prices are down 50%, even if house price indices don't yet show it.

Last week's announcement by the Green Party that an 80% windfall tax on rezoning of land would be introduced also drew ire from the property sector. "Stalin rises from the dead," was the blunt text message response from one developer.

"It'll make zoned land dearer, because people will want to avoid the tax," said one industry veteran. "When it comes to taxation issues, everything seems to be property-related. You can't take blood from a stone. Why would you bother getting anything rezoned now? How do you calculate the tax? Do you take into account hope value? There's no money in property. That's why we have Nama. They're locking the stable door after the horse has bolted." He said the government was "rudderless" and the windfall tax "bonkers".

One partner in a property advisory company said he might as well quit if it's passed. He said there were lessons to be learned from other development land crashes.

"This has happened before, in the UK. The land market collapsed between 1987 and 1988 and recovered in three years. The difference here is that the banks don't have any money. What's happening here is not what's happening in Britain at the moment," he said.

Instead, he said, the few remaining developers with cash in Ireland are investing money in return for a guaranteed percentage in any upswing in site value they create. A site that was worth €50m might now be worth €15m but the banks were agreeing that, if somebody put in €2m in cash, they'd take 15%-20% of future profits.

"The banks are doing that. It's the only way deals are being done," he said.

The main hope of shifting worthless development land lies in bundling it with investment-producing properties or land in areas where people want to live. Finance minister Brian Lenihan said that had been the experience in the United States "and that is exactly what we envisage".

"Nama will have the capacity to dispose of a whole part of a portfolio, so the bad and the good will be disposed of in the one operation," Lenihan said.

If that doesn't tickle the fancy of private equity players, then compound interest alone on the bond coupons will make it nigh on impossible for the state to emerge from Nama without losing any of the few remaining threads in its shirt.