From unfettered optimism to dark and dismal thoughts...it's pretty hard being the leader of the Scottish LibDems

The statistics are hideous. First they lost 11 of their 16 MSPs in 2011, then 80 of their 151 councillors in 2012, then their only MEP in 2014, and finally 10 of their 11 MPs last year.

As bad runs go, it’s something of a classic. Yet Rennie is eerily upbeat about next month’s poll and says his party is “turning the corner”.

In part, it’s about no longer being shackled to the Conservatives. Asked if he’s glad to be free of them, despite the loss of power, he laughs: “Oh, God aye. Because you actually find out what they’re like when you’re with them.”

He cites the attack ads depicting Alex Salmond as a pickpocket last year as an example.

“They were trying to say Scotland were going to pick pockets. It was nothing do with Alex Salmond. It was all about Scots. I thought that was disgraceful.”

Agreeing with the SNP, he says the Tories also tried to short-change Holyrood by £7bn when setting the fiscal framework for Scotland’s new tax powers.

“They were playing to their Ukip, English nationalist element,” he grumbles.

And despite Nicola Sturgeon continuing to raise the coalition whenever Rennie is in the room, he feels that line is becoming “tired and boring” and losing traction.

“Some people will never forgive us and I accept that. But time solves some of that.”

Since emancipation from Tory serfdom, he says he’s gone from being “defensive and cautious” in the general election to “confident, positive, ambitious” this time around.

But doesn't your pitch to voters - LibDem ideas can make Scotland “the best again” - start from the doom-laden premise that Scotland is declining on multiple fronts and needs rescued?

“Yes, but it’s about being the best again,” he says. “It’s about lifting our heads up. Because we’ve been distracted by independence, things have slipped back. I want to get Scotland back up there, with an ambitious programme for investing in education with a penny on income tax.

“Protecting our civil liberties, getting our police force to be the best again so that it’s got the confidence of the public but also police officers themselves.

“On the environment, making sure we have a very strong programme on fracking and not cutting Air Passenger Duty [as the SNP would]. And on the health service, making sure mental health services get the support they need and recruiting more GPs. You couldn’t be more positive than that.”

The most important strand is education, with a proposal to put 1p on all three income tax bands to raise an extra £475m. Why not a 50p top rate like Labour?

He concedes Sturgeon has a point when she warns hiking bills for the rich could cause some to leave Scotland and reduce the overall tax take.

“We want the money guaranteed. Schools, colleges and nurseries desperately need it, so we don’t want to take a gamble with the 50p rate when we’re not absolutely convinced that it’s going to raise the money we need.”

So aren’t you being harsh on Sturgeon when you accuse her of being timid on tax?

“Oh, she is incredibly timid,” he whistles. “Not to change any income tax rates at all? That’s timid. Really timid. Depressingly timid. And all the lectures we’ve had about austerity!"

He says it’s an insight into the SNP’s ultra-cautious approach to securing independence.

“I think she’s been trapped, because she’s got the powers, she could invest in education, but she’s choosing not to. So her timidity, which has always been there, is now exposed.

“It reveals her inner belief - do nothing until you get independence. I think the SNP’s rhetoric and their action hasn’t matched for some time and people are now beginning to see it.”

He’s off on a bit of a riff now, casting the LibDems, despite their notorious political promiscuity, as bastions of principle and the SNP as shallow chancers.

“We say things even though they might be unpopular - decriminalise drugs, for instance. Whereas [Sturgeon] only says things if it gets independence. It’s important to have conviction at the heart of your party, otherwise you just end up drifting. She’s not prepared to say anything that people might disapprove of. She’s an empty vessel on so much of public life because the ultimate goal is to get towards independence.”

Education is critical for another reason. In 2011, the SNP poached thousands of LibDem votes by exploiting disillusion over the party’s broken promise not to raise tuition fees. The emphasis on education in 2016 is meant to woo back some of that lost vote.

“We had a lot of educationalists in the party, professors, academics, students,” Rennie says. “That central core of our policy was adversely affected during the coalition, but we’re slowly starting to scrape that back. I’m not saying they’re flooding over yet, but I think the foundations are there… it’s turning the corner.”

Talking of turns, the LibDems performed a swift 180 last month, backing fracking at their spring conference, followed by the leadership announcing a ban. What happened?

He admits he blundered by not anticipating how the conference vote would go - he even nipped out for a photo-op while it took place - and realised instantly he had to overrule it.

“I wanted a clear, distinctive position on the environment. We’re not going to open up a new front in carbon-based fuels. So I changed the party policy, to some discomfort in the party.”

Did you get a lot of grief? “Och aye. But you’re leader, eh? You need to do it sometimes.”

Although Rennie lost 10 MPs last year, his party’s vote share held up pretty well in most of the seats it defended, but was simply overtaken by the SNP tsunami.

The party won five MSPs last time, but is in danger of being pushed into fifth place or worse by the Greens and Ukip. What will success look like on May 5?

“I never predict. I’ve got a number in my head but you’re never going to see in my head.”

You think you’ll advance? “Yes. Yes, I do. I believe we’ll grow”.

His optimism extends to saying the party might even regain Edinburgh Western, where a financial scandal is lapping around local MP Michelle Thomson, formerly of the SNP.

There are also “good campaigns” (he doesn’t say winning ones) in former LibDem seats in the Highlands, Aberdeenshire and Argyll & Bute, as well as hopes of returning list MSPs in Glasgow, Central Scotland and the West of Scotland.

What about the elephant in the room? What about the Northern Isles, where Tavish Scott and Liam McArthur are trying to hang on amid the stink of Orkney and Shetland MP Alistair Carmichael being taken to court for lying over the leaked ‘Frenchgate’ memo?

“It’s good at the moment. The Alistair thing is coming up from time to time,” he says.

He says Carmichael made “a mistake” and calls his lie an “aberration”, but strongly defends him as “fundamentally a decent person” with much still to contribute to the party.

Carmichael was left with a £150,000 legal bill after his narrow escape from election court. Did you give any money to his legal fund? “Yes, I contributed.” How much? “I’m not going to tell you.” Too embarrassed to say? “All right, £750. I’m not a rich man but I felt it was important.”

Rennie squeaked into Holyrood in 2011 with just 5.9 per cent of the list vote in mid-Scotland and Fife. This time he’s on the list again, but also standing in the North East Fife constituency, trying to overturn an SNP majority of 2592. Neither route back to parliament looks safe.

What happens if you don’t get in? “Dark, dismal thoughts, Tom.” But not far-fetched. “I’m going to win. I’m going to continue to be leader. I’m going to be the MSP for North East Fife, my home patch. So I’m going to win.” He later modifies this to “a good chance of winning”.

If he is rejected by the voters, the Scottish LibDems have a trusted solution. Lord Jim Wallace, Lord Nicol Stephen, Lord Jeremy Purvis. Lord Rennie next perhaps?

“I’m not going there,” he says, meaning the subject not the place. Would you not go to the Lords on principle? “This is where my focus is.” But you have to think ahead like anyone else with a mortgage. “If Nicola can say she’s not got a Plan B, I can say I don’t have a Plan B. I’m focused on the Scottish Parliament, winning the North East Fife seat, providing a strong Liberal voice for the next five years. That’s what we’re about.”

Still, as he walks away, it’s impossible not to picture a comforting ermine robe chasing after him.