As if Gordon Brown hasn’t enough on his plate at the moment, this morning he received a letter from the Home Builders Federation telling him that his housing policy doesn’t stack up.

The letter sent by HBF Executive Chairman Stewart Baseley warns Mr Brown that he faces stark choices between the 240,000 a year housing target, aspirations for more affordable housing, private sector support for funding infrastructure, the zero-carbon target and a selection of other policy objectives such as lifetime homes. The HBF message is simple: “You can’t have it all.”

This rather holes the current housing strategy below the water line and is likely to prove embarrassing for the government, as it felt that it had the house builders on board. The government was banking on squeezing large sums out of private developers in exchange for granting planning permission to pay for extemely ambitious housing plans.

But it seems the sums no longer stack up as the housing market has gone into reverse.

In the latest issue of Housebuilder magazine, John Stewart, HBF’s director of economic affairs, puts together some interesting numbers showing the approximate additional cost per hectare to house builders of meeting the government’s aspirations. He estimates that the cost of the “regulatory burden”, not including the latest pronouncement on lifetime homes, to be more than £2.5 million per hectare – or put another way more than £60,000 a home.

It will be interesting from here to gauge how confident Caroline Flint or Gordon Brown are about meeting the target of 240,000 zero carbon homes by 2016.