Tim Farron is facing the first crisis of his leadership of the Liberal Democrats, as senior activists consider quitting the party over his decision to vote for air strikes in Syria.

Former MPs have also made it clear that they would have voted against the action, while members of the party’s powerful Federal Policy Committee (FPC) are angry that Mr Farron did not consult it about voting with the Government.

Many activists joined the Lib Dems because of the late Charles Kennedy’s opposition to the Iraq war in 2003 and were stunned when Mr Farron did not oppose air strikes against Isis in Syria. Mr Farron was one of the six Lib Dems who backed the attacks; only his former leadership rival, Norman Lamb, and Ceredigion MP Mark Williams voted against.

Gareth Epps, a member of the FPC who stood against David Cameron in Witney at the 2001 general election, said he is minded to let his membership lapse at the end of this year. He said: “For a party that has prided itself on enlightened scepticism of Western-led military adventurism, they [the Lib Dem leadership] seem to have suspended all critical faculties.”

Mr Farron set five tests that the Prime Minister had to meet before he would vote for air strikes, including legal cover from the United Nations and a reconstruction plan for when and if Isis is defeated in Syria. Mr Epps and other activists disagree that these tests were passed before last week’s vote.

British jets prepare for air strikes in Syria Show all 10 1 /10 British jets prepare for air strikes in Syria British jets prepare for air strikes in Syria A Tornado jet takes off from RAF Lossiemouth in Scotland, as RAF Tornado jets carried out the first British bombing runs over Syria British jets prepare for air strikes in Syria Pilots and ground crew prepare combat aircraft Panavia Tornados at RAF Marham at RAF Marham, UK Getty British jets prepare for air strikes in Syria A Eurofighter Typhoon jet takes off from RAF Lossiemouth in Scotland, as RAF Tornado jets carried out the first British bombing runs over Syria British jets prepare for air strikes in Syria A RAF Tornado arrives at RAF Akrotiri to begin operations in Akrotiri British jets prepare for air strikes in Syria A Tornado jet ahead of taking off from RAF Lossiemouth in Scotland, as RAF Tornado jets carried out the first British bombing runs over Syria, the Ministry of Defence has confirmed. The air strikes were carried out within hours of a vote by MPs in the Commons to back extending operations against Isis from neighbouring Iraq British jets prepare for air strikes in Syria Personnel work on a British Tornado after it returned from a mission at RAF Akrotiri in southern Cyprus British jets prepare for air strikes in Syria Two RAF Tornado GR4's, both with remaining weapons ordnance, approach RAF Akrotiri in Cyprus, as they return to the base after carrying out some of the first British bombing runs over Syria British jets prepare for air strikes in Syria A RAF Tornado takes off from RAF Akrotiri, on the Mediterranean island nation of Cyprus British jets prepare for air strikes in Syria A Tornado jet leaving RAF Lossiemouth in Scotland British jets prepare for air strikes in Syria AKA RAF Tornado arrives at RAF Akrotiri to begin operations in Akrotiri, Cyprus. The RAF has sent two further Tornado aircraft and six Typhoons to bolster aircraft now flying sorties to both Iraq and Syria

David Grace, chair of Liberal Democrats for Peace and Security, said that he had considered resigning; while many activists have stated on social media that they are also thinking about quitting. Mr Grace added: “The great feeling is [that] the leadership could have consulted more widely.”

Norman Baker, the former Home Office minister who lost his Lewes seat at the election, posted on Facebook that, “for the record”, he would have voted against the air strikes. He added: “Have we learnt nothing from the last 15 years?”

RAF planes launch second round of strikes on Isis oil field in Syria

Andrew George, an MP for 18 years until losing to the Conservatives in May, added: “If I were in Parliament today, I would vote against UK bombing in Syria. I withstood intense pressure and party whips two years ago when I spoke up and voted against military action in Syria then. We defeated the Government. It was the right thing to do.”

Julian Huppert, who narrowly failed to retain Cambridge, also opposed air strikes in 2013. He said: “In 2013, I surveyed as many people in Cambridge as I could. Most agreed with me to oppose bombing. Not aware anyone has asked this time.”

Stephen Lloyd, the former MP for Eastbourne, argued that there was no long-term plan for the region, meaning bombing would be “counterproductive”.

He added: “My fear is [that] our determination to join the effort, without a clear endgame, stirs memories of many a ‘drumbeat to war’ in the past, without any real idea of what would be a practical and achievable conclusion.”

The FPC meets this week, and several members want to discuss why it was not consulted thoroughly. Many also think that the party’s other most senior committee, the Federal Executive (FE), should have been better advised of Mr Farron’s thinking.

A FPC member said: “On an issue of this sensitivity and significance, Mr Farron should have consulted the party. The leadership should have spoken to the FE and FPC – after all, the FE got Charles Kennedy to go out on his finest hour, the march against the Iraq war.”

Mr Epps has also asked the FPC to discuss “the details within its remit arising from the Syria situation” at the meeting.

Norman Lamb was one of only two Lib Dem MPs to vote against the airstrikes (Getty) (Getty Images)

Another FPC member said: “A lot of people are quite unhappy with the vote. I think there will be a body of opinion who think that [the situation was mishandled].”

Separately, the FE has also received a long-awaited review into the Lib Dems’ election disaster, which saw them reduced to eight MPs from 57 in 2010. The conclusions and recommendations of this report are being discussed by the FE this weekend.

Despite criticism from within the Lib Dems, Mr Farron has been praised by some activists and members of other parties for his speech on the air strikes at Wednesday’s debate in the House of Commons.