Comparing the SNP to the Tories, Mr Farron claimed finding a way to combat Scottish nationalism would create a “movement” able to win against its English counterpart in 2024.
Speaking to The Scotsman, Mr Farron criticised the ideologies of both administrations, adding he was “deeply concerned about the ongoing division mooted and stirred” by the SNP.
He continued: “The problem is when you get into the politics of the flag, people will forgive you anything and everything.
“This is a real test for progressives – the Liberal Democrats and Labour – under more impressive leadership than it was in Scotland.
“Are we able to give Scotland the hope of a Britain led by progressives who will fight for everybody, unite the country, invest in health and social care, and tackle the things that all of us care about more than those narrow obsessions?
“The Scottish elections now are an opportunity for progressive voters in Scotland to do what I hope we can do across the whole United Kingdom in the run-up to the 2024 general election across the UK, and that is to vote intelligently.
“It’s the opportunity to potentially begin a movement that might rescue Britain from Boris in a way that is infinitely less heart-breaking than damaging and separating the country.
“If we can work together intelligently on the voter level in Scotland to defeat Scottish nationalists, then maybe we can be the English nationalists.
“It’s a bit like in Independence Day where they first get through the force field – ‘ah, we now know we can do it’ – then go and do it everywhere else as well.”
Mr Farron also criticised Boris Johnson over his performance at Prime Minister’s Questions this week that saw him refuse twice to answer how he paid for renovations to his Downing Street flat.
The Prime Minister has been accused of being loaned the money by the Tory party before paying it back.
Questioning his answers, the Lib Dem MP said: “He was rattled. I’m not sure [Labour leader Sir Keir] Starmer scored that many points, but golly he got to Boris Johnson.
“I thought his performance was terrifying really and you know all the people being trotted out defending him, people like Nadhim Zahawi having to trash his own credibility to defend the indefensible.
“Boris Johnson might well survive because there's no justice, but we have to just keep fighting anyway because we can't lie upon the Tory party adopting a conscience, we have to defeat them.”
The Westmorland and Lonsdale MP admitted he understood people’s frustrations with Westminster, but that independence would devastate him and his constituents.
He explained: “As an MP for somewhere very close to Scotland and as somebody who is a northerner, I am thoroughly opposed to identity politics because I think you just end up hiding behind your flag or your badge rather than seeking what unites us.
“I feel far more in common culturally and outlook wise – and let’s be honest, resentment towards Westminster-wise with people in Scotland – than I do in the South-East of England, so I think there's a general sense here on an emotional, but also practical level that breaking up the United Kingdom would be an absolute tragedy.
“It would break the hearts of most people I represent, the ones I grow up with and me as well.
“The potential of a hard border that would absolutely impact upon people's lives is very real and Nicola Sturgeon’s had weeks to come up with a half decent answer and she hasn’t.
“That’s troubled loads of people who live in Cumbria, but work in Scotland or vice versa.”
The 50-year-old also had kind words for another former Lib Dem leader Jo Swinson, who lost her seat in 2019.
Ms Swinson, who had originally been a favourite to succeed Mr Farron in 2017 following his resignation as party leader, only lasted in the party’s top role for five months when she was elected to the position leading into the 2019 general election.
Revealing they were still in touch, Mr Farron suggested Ms Swinson was not rushing to make a political comeback.
He said: “We are definitely still taking. Her advice is something I proactively go and seek, she’s a very good friend.
”But she has to make her own choices. There are other things to do in life.
"Even being leader of the Liberal Democrats is not the most important thing, I’ve discovered.”