Sir Vince Cable has spent the morning writing the penultimate chapter of his first novel. The latest in a line of politicians to turn to literature, he’s confident his predecessors have not set the bar too high. “Iain Duncan Smith’s was terrible. And there was this other woman...” Louise Mensch? “No, she’s even worse!”

Cable is back in Cambridge to speak at the debating society of his alma mater, Fitzwilliam College, where he studied Natural Sciences, before defecting to Economics at Part II – mostly, he tells me, in order to free up his afternoons for the Cambridge Union and amateur dramatics.

A former Union president, he recalls “disgracing himself” with a term card which featured “lots of comedians and quite a few criminals”. The Kray twins cancelled a few days before they were due to appear. Another speaker, he sheepishly admits, was subsequently hanged.

When I bring up recent protests against the Union’s hosting of Julian Assange and Germaine Greer, his face creases into a frown. “I think it’s terrible. Greer was one of my great contemporaries, and a marvellously talented and interesting woman. The idea that people like that are being barred is terrible.”

For him, Fitzwilliam, which relocated to Castle Hill in the year Cable sat his finals, has changed almost beyond recognition. As a “northern grammar school boy” – an identity he reprises with a touch of pride – he admits to feeling like a fish out of water on his arrival.

“It was quite public school dominated – although I was in no sense under-privileged, we did tend to think of ourselves as the proletariat in this place. In a way, that gave us a bit of an edge to be more competitive... but I did feel quite intimidated.

“I’d never been in a place before where you actually met people who had been to Eton and dressed up in hunting gear and things like that. I mean, it was a bit like visiting the zoo sometimes.”

And probably quite a good preparation for Parliament? He smiles and raises his eyebrows.

“Yes... probably quite a good preparation for Parliament.”

Cable may still be an astute political commentator but, after the surprise loss of his seat in the 2015 general election, it seems he has put his Westminster career behind him.

He is unreserved – often cheeky – with his political observations, and he describes his experiences of the Westminster crowd with all the exactitude of an avid people-watcher. He calls David Cameron a “cold fish... very comfortable with the Bullingdon Club image”, whereas George Osborne, apparently, is “more self-conscious”.

Unprompted, he falls into a critique of his party’s naivety when working with the Conservatives. “What we didn’t realise is that, when it comes to destroying their enemies, the Tories are absolutely ruthless. And they’re about to destroy Labour... although they’re getting quite a lot of help on that front.”

At the time, one newspaper article described Cable as the “moral core” of the Conservative-Liberal Democrat coalition. “It’s a flattering way of describing it,” he says. “I was a bit bloody-minded, I think, which is probably more accurate. I was uncomfortable working with the Tories, but I thought we had no choice.”

If he has regrets about the way in which the coalition was conducted, Cable is magnanimous when asked if, with retrospect, he would go back and make the decision to form one.

“I think Nick Clegg was right, but of course we’ve paid a terrible political price. And it’s yet to be seen whether we will recover. There’s this enormous political space in the UK between the Tories and Corbyn, which someone should fill, and we’re waiting to fill it.”

I ask if the new Liberal Democrat leader, Tim Farron, who has previously taken controversial stances on gay marriage, is the right man to win over a centre-left. “Well, I think what you’re hinting at is that he’s an evangelical Christian...” Cable looks wary. “I don’t see why that’s a problem: issues like abortion should be matters of personal choice.

“I happen to have liberal views and always have had, but I don’t mind working with someone who is more traditional and religiously guided.” He’s keen to draw attention to Farron’s status as “a radical liberal in the old tradition”.

“On some of the big moral issues, refugees, Middle Eastern wars, he’s very much in the radical camp.”

Given that Cable has been credited by many as the only politician to have foreseen the financial crisis, predictions like these are worth our attention.

George Osborne will be the next Prime Minister, he tells me, “all other things being equal”.

He seems, perhaps surprisingly, far less concerned by this than by the prospect of the impending referendum on the UK’s EU membership. “I think Cameron has miscalculated horribly by having the referendum, and then imagining that this renegotiation, with these frankly rather flimsy issues, would somehow persuade a lot of sceptical people.

“I think there is a very high risk of losing, and the consequences would be very bad and very profound.”

Later, Cable delivers the sort of economic forecast Jeremy Paxman might describe as a “veritable smorgasbord”. Comparing the 2008 financial crash to a heart attack, he warns that today’s economy “is still connected to the life support system”, and calls upon the political left to resist the Tory-built historical narrative that the financial crisis was the fault of the Labour Party.

He is critical of the Chancellor’s ‘long-term economic plan’, even if government cuts are not, thus far, as drastic as they threatened to be prior to the general election. “George Osborne’s found some money down the back of the sofa,” he concedes. “But,” he adds darkly, “What the sofa gives, the sofa can take away.”

Cable may have abandoned Westminster for the fictional world of the political thriller. But serious challenges lie ahead for characters in both realms, and it seems a shame that such an experienced and talented politician can only shape the ending of one of these narratives.