Boris Johnson faces a fresh headache over planning reforms, with Conservative MPs urging the prime minister to change course in the wake of the party’s shock defeat in the Chesham and Amersham byelection. Pressure is expected to build on Johnson on Monday in a parliamentary debate called by Labour on the changes, as MPs demand better protections for communities to have their say over planning applications. Conservative MPs, including the former prime minister Theresa May, have criticised the proposed measures, which include stripping elected planning committees of development decisions and making it easier to obtain automatic consent, intended to significantly boost housebuilding. Moves against the plans are being coordinated in parliament by the former environment minister Theresa Villiers. Labour will challenge backbench Tory rebels to vote for its changes to mark their opposition to the plans, though even Conservatives who oppose the measures will be loth to hand a PR win to Labour by voting for its motion. The justice secretary, Robert Buckland, said the planning reforms were being “mischaracterised” when he was shown a leaflet used by the Liberal Democrats before Thursday’s byelection containing May’s claims that the plans risk the “wrong homes being built in the wrong places”. “Our policy very often was very frankly mischaracterised. At no time has this proposal been about suddenly indiscriminately bricking over the countryside,” Buckland said on the BBC’s Andrew Marr show on Sunday. “I think the policy is absolutely right. What it’s designed to try and do is make sure we get that balance across the country.” Steve Reed, the shadow communities and local government secretary, said: “Voters have shown Conservative MPs what they think of the developers’ charter. Those MPs now have the chance to join Labour in voting to kill off these perverse reforms once and for all.” Ed Davey, the Lib Dem leader, said his party was not against housebuilding. “Well, I’m actually a Yimby – yes in my back yard. And what that means is you need a planning process that will deliver those houses with community consent,” he said. “The Liberal Democrats have neighbourhood plans which communities can lead on and do produce the houses we need, the social affordable houses that communities want.” Peter Fleet, the Tory candidate who lost the Chesham and Amersham byelection, said the presentation of the changes had meant the Lib Dems could capitalise. “The Lib Dems repeatedly claimed that changes would give greedy developers ‘a free hand to build whatever they want’ across the Chilterns,” Fleet wrote in the Sunday Telegraph. “It did not help our cause that prominent Conservatives were quoted front and centre of the Lib Dem leaflet which advanced this pernicious charge. As a party we need to do better at conducting our policy debates in private. “I argued that the planning bill would help speed up the redevelopment of brownfield sites for the construction of affordable housing in Chesham and Amersham while providing important protections for our green open spaces. Ministers must ensure that this is how the bill can be presented.”