Coalition plans to allow homeowners to build large extensions on their homes without planning permission suffered a set-back today after they were overwhelmingly rejected by Liberal Democrat activists.
The vote comes amid growing opposition to the scheme among Conservative councils and MPs who warn that it will provoke bitter disputes between neighbours and lead to ugly developments.
Under the scheme, which is part of a proposed package of planning reforms, householders would be allowed to build extensions and conservatories up to 8m long without approval from their councils - twice the current limit.
Ministers say the move will help to create jobs by providing extra work for the building industry.
But Liberal Democrat councillors lined up at their party conference to denounce the plan.
Catharine Smart, from Cambridge, protested: "You just wonder what planet some of these people are on."
She said: "Just for once these parliamentarians should listen to the little people on the district councils who actually know most about this. Just listen to them and take these stupid ideas away."
Prue Bray, from Wokingham, Berkshire, said: "Surely it is not beyond us as a party to come up with a better way for the party and parliamentarians to work together so we can avoid situations like this?"
A motion condemning the moves was backed by almost all delegates as the Local Government Minister, Don Foster, suffered the embarrassment of being the only speaker against it.
Although today's vote is not binding on the party leadership, Liberal Democrat ministers are expected to seek changes to the planning proposals.
In a statement after the vote, Mr Foster said: "We are now consulting on how the planning regulations will work in practice and we will be listening to the views expressed today by conference, which will form an important part of this process."