It is widely expected the Zero Carbon Task Group which seeks to define zero-carbon housing and headed by Barratt CEO Mark Clare, will recommend that small or difficult sites be exempt from meeting the highest levels of the Sustainable Homes Code by paying a carbon levy.

This charge would be used to pay for equivalent carbon savings in other areas, such as improving the existing housing stock.

All homes must be zero carbon by 2016 under UK building regulations.

Sources close to the task group said it would report that the challenges of reaching zero carbon are different for large, medium and small sites.

It will argue that small sites will find it impossible to reach level six as they are not large enough to make combined heat and power systems work and do not have scope for other forms of renewable energy generation.

A source close to the group said: “This is a sensible and pragmatic approach as to how we meet the zero-carbon obligation.”

Paul King, chief executive of the UK Green Building Council, refused to confirm the details of the group’s recommendations but said: “The aim is to come up with a mechanism that does not dumb down the commitment to zero carbon, but does provide equity between large and small sites.”

The task group backed by the UK Building Council will present their findings to ministers on Tuesday.