Liberal Democrat members have handed a very public rebuke to Ed Davey before his key speech to the party conference, rebelling in large numbers over a plan by the leadership to scrap national targets for housebuilding. In a first tangible sign of internal pushback against the Davey-led idea of shaping the Lib Dems’ policy platform to tempt wavering Conservative voters to backing the party in so-called “blue wall” seats, members voted to maintain a target of 380,000 homes a year. In sometimes angry scenes at the gathering in Bournemouth, the former party leader Tim Farron was booed for arguing that the target, which he called “vague and vacuous”, should be scrapped. Davey has already committed to not building on green belt land, described by officials as an offering to previous Tory voters who are considering a move to the Lib Dems. The frontbench motion on housing pledged to build 150,000 social rent homes a year, as well as measures for renters such as longer-term tenancies, but got rid of the wider national housebuilding target. Helen Morgan, who speaks for the party on housing and communities, argued that it was better to create local targets to “bring communities with us”, given the national version had “been in place for decades, and has utterly failed to deliver the homes we need”. But in a blow to Davey’s authority, an amendment tabled by the Young Liberals to restore the 380,000 target was overwhelmingly passed. Janey Little, chair of the Young Liberals, won loud applause for arguing that scrapping it risked alienating younger voters who were “fearful for our futures when homes are so unaffordable”. Farron, who led the Lib Dems for 2015 to 2017, was booed for a passionate speech in which he called national housebuilding targets a gift to developers, and the “most rightwing thing I’ve seen at party conference since we sent Liz Truss off to work undercover”, a reference to Truss’s past as a Lib Dem. In a brutal rejoinder, illustrating the tensions even at the top level of the party, Rob Blackie, the party’s candidate for London mayor, then lambasted Farron: “That speech was beneath you. Tim – we are better than that.” Stephen Robinson, the leader of Chelmsford council, warned that scrapping the target could prove as corrosive as the party’s decision to back university tuition fees in coalition. “Getting rid of a target that we only voted for two years ago will lose the votes of young people, who will feel betrayed by the Liberal Democrats for the second time in 10 years,” he said. While such arguments and policy defeats are not unusual at Lib Dem conferences, which are notably more democratic than the highly choreographed Labour and Conservative versions, the vote marks a risk for Davey in his general election tactics. In his speech to the conference on Tuesday, Davey will reiterate the intention to win Tory-held seats, saying: “We have taken big chunks out of the blue wall. Our job now is to bring it tumbling down. “The British people are desperate to see the back of this appalling, out-of-touch Conservative government, and we are the ones who can make it happen.” The Conservatives, he was to say, were “more like a bad TV soap opera than a functioning government”. “The factions and the feuds, the personal vendettas, the shock exits and unwelcome returns, the total lack of connection to reality, each episode worse than the last – well it’s time to change the channel,” he will say.