Developers may find it more difficult in the future to claim they have no need to provide affordable homes on new sites in West Dorset and Weymouth and Portland.

Dorchester councillor Molly Rennie told district council colleagues that she wanted to avoid a repeat of the county town prison scheme where the developer successfully argued that the project would not be viable if they had to include affordable homes.

Planning policy manager Trevor Warrick told her that the concerns were shared by the Government which is proposing new rules in future legislation.

“We need to look at the whole question of viability. Developers have raised it with us, as you might expect, but as a council we need to look at our policy on it,” he said.

Cllr Rennie raised the issue on Tuesday during a presentation about the review of the Local Plan which will guide development in West Dorset and Weymouth and Portland until 2036.

The document should be finalised by the end of July with a public consultation on its proposals taking place between mid-August and October.

Amongst the suggestions are the need to find sites for almost 19,000 new homes and 15,000 new jobs over the period of the plan.

The revised local plan seeks to maintain the current level of affordable homes in new developments of more than ten homes – 35 per cent in Weymouth and Portland and West Dorset and 25 per cent on Portland.

Mr Warrick, said that developers seeking less would be challenged with an “open book” approach where they would have to spell out their finances to make a case for less than the minimum level.

The new proposed policy reads: “Applicants seeking to justify a lower level of affordable housing provision will be expected to provide an assessment of viability, which should adopt an ‘open book’ approach and take account of grant funding or any other subsidy. A lower level of provision will only be permitted if: the assessment shows that it is not economically viable to make the minimum level of provision being sought; and there are good reasons to bring the development forward.”

Changes to several policies are being discussed including definitions of affordable housing for the area; protection of the environment; sites for wind turbines and solar ‘farms’ and definitions for ‘sustainable development’.

Councillors were told that the draft local plan review document was likely to change before being adopted because of proposals currently being discussed by the Government.