Mr Farron, a committed Christian, faced repeated questions over his attitude to homosexuality during the general election campaign last year, which overshadowed the party’s attempts to win back voters by capitalising on anger among pro-Europeans.
Pro-EU MPs hit out at Mr Farron when it emerged that he had missed a series of votes during a dramatic night in the Commons, where Theresa May narrowly saw off a backbench rebellion to a key piece of Brexit legislation.
Mr Farron apologised for attending the event at Sherborne Abbey, in Dorset, entitled ”Illiberal Truths” on Monday night, saying the party had expected Labour to abstain so he had been granted permission to conduct a longstanding engagement.
The event description said: “Tim Farron MP made the headlines during the 2017 general election campaign as leader of the Liberal Democrat party, although it was not, in fact, politics that generated the headlines but repeated attempts by the mainstream media to get him to express an opinion on whether gay sex was compatible with Christian faith.
“He announced he would step down as party leader following the election, stating that he had become “torn between living as a faithful Christian and serving as a political leader”.
“Many hold strong opinions on the issue but it raised an even more important question: What happens when my truth is not yours?”
Come and hear @timfarron @SherborneInsite explore #Faith #Belief and #SharedValues in Illiberal Truths: https://t.co/5BHSKOibbc. What happens when my #truth is not yours? Come and find out! https://t.co/1dIiT4Zbhg @DioSalisbury @BathWells pic.twitter.com/xbvA3EUb95— Sherborne Insight (@SherborneInsite) July 11, 2018
The well-attended event was described as a “wide-ranging lecture on values and contemporary society”, which did not feature questions on homosexuality or Mr Farron’s resignation, according to attendees.
Mr Farron said in a statement: “I was authorised to be absent due to a pre-arranged engagement away from the parliamentary estate.
“In the end nobody expected the vote to be as close as it was – I’d actually cancelled the engagement earlier on, but then un-cancelled because we expected Labour to abstain and the government to win by miles.
“We clearly called it wrong, as did Labour. I take full responsibility for my part. The Tories don’t deserve any luck, I’m so sorry I inadvertently granted them some.”
Lib Dem leader Sir Vince Cable also missed the votes to attend a meeting off the parliamentary estate, sources confirmed.
A party source told The Independent: “Vince had an important meeting off the parliamentary estate, which had been sanctioned by the whips long before these amendments were up for the vote.
“The Chequers compromise is unworkable. It is still unworkable with the amendments last night.”
“Giving a £5 lecture on how you can’t be a gay Christian?”
Aberavon MP Stephen Kinnock tweeted: “Last night two Brextremist-driven amendments were carried by a whisker – 3 and 4 votes, respectively. 14 Tories rebelled.
“Tim Farron and Vince Cable (those doughty, fearless crusaders against a hard Brexit) didn’t vote.”
And shadow justice secretary Richard Burgon added: “Journalists reporting current Lib Dem Leader Vince Cable and last Lib Dem Leader Tim Farron didn’t vote in one of tonight’s votes in which Tory Government only survived by 3 votes.
“Last week they brought a motion to get in to Government with the Tories. #NeverTrustTheLibDems.”
Mr Farron resigned as leader of the Liberal Democrats last year following a long-running row over his views.
In a statement at the time, Mr Farron said: “I seem to be the subject of suspicion because of what I believe and who my faith is in.
“In which case we are kidding ourselves if we think we yet live in a tolerant, liberal society. That’s why I have chosen to step down as leader of the Liberal Democrats.”
He said that from the “very first day” of his leadership he had faced questions about his Christian faith and that he had tried to answer with “grace and patience”, adding: “Sometimes my answers could have been wiser.”
It comes as Ms May faced the biggest rebellion of her premiership on Monday night, as 14 Tory rebels voted against Eurosceptic clause that would prevent the UK collecting tariffs on behalf of the EU unless it agreed to do the same.
An amendment that would stop the UK from joining the bloc’s VAT regime drew 11 Conservative rebels, but Ms May scraped through with the support of three Labour MPs, Frank Field, Kate Hoey and Graham Stringer, on both.