Senior Lib Dems warned their party against backing the December election that Boris Johnson had been demanding, it has emerged.

Vince Cable, Tim Farron and Phillip Lee are all said to have raised serious concerns about the party’s surprise move to offer the prime minister the chance of an election. Opposition parties had previously been united in opposing the move.

It is understood they told party officials that keeping Johnson locked in a minority government, inflicting parliamentary defeats and fostering Tory infighting would have given them a much better chance to plan and fight an election in the spring.

The Observer broke the news that the Lib Dems, along with the SNP, were planning to offer Johnson a December election. Once they made the offer, Labour opted to back the 12 December election a few days later. Lib Dem insiders said there was resistance to the December election plan, warning that supporters of the idea had become obsessed with internal polling in the wake of May’s European elections suggesting the party would be competitive in well over 100 seats. “Hubris was the problem throughout,” said one.

The election ended in disaster for the party, with leader Jo Swinson losing her seat and the Lib Dems finishing with one fewer MPs than in 2017 – an outcome unthinkable at the outset of the campaign just six weeks ago. Swinson has blamed the decision by the Brexit party to pull out of many seats for the Lib Dems’ struggles, while others believe her exclusion from televised leaders’ debates was a key development. Defeated Lib Dems also pointed to the party’s unpopular pledge to revoke Brexit without a referendum.

Swinson and the former Liberal Democrat justice spokesperson Phillip Lee on a visit to Shinfield Tennis Club on December 7. Photograph: Aaron Chown/PA

Lee, who lost in Wokingham despite a large swing to the Lib Dems, confirmed he had opposed an election. “Having the election in the first place was a bad decision,” he said. “I did my best to try to stop that because we hadn’t exhausted the effort to get the last parliament to back a people’s vote. We bet the house on Nigel Farage not stepping aside. On the doorstep, our unnecessary revoke policy put us on the back foot and our national campaign didn’t cut through to people. We were also fighting fear of Corbyn. In defence of our party, we had great policies, particularly around childcare, climate change and energy efficiency, and mental health services.

“But as soon as the BBC decided not to be impartial and to frame the choice as Corbyn versus Johnson, the game was over. For the future, the liberal progressive centre has to present a credible alternative to rightwing populism and nationalism.”

However, party sources said the “prevailing view” was that the Lib Dems had to back an election because there were signs Johnson had the votes to force through his Brexit deal. There were also concerns that the EU would not allow another Brexit extension.

The Lib Dems are now in search of a new leader, with MP Ed Davey and peer Sal Brinton taking temporary charge. The Oxford West and Abingdon MP Layla Moran is seen as the favourite to replace Swinson.