I met Peter Mandelson twice and saw his Jekyll and Hyde personality first-hand - Andrew Vine

That opinion of him became inescapable across the course of two long days I spent with Mandelson during the 1997 and 2001 general election campaigns. Forbidding one minute, approachable the next, here was the slipperiest politician I’ve met in 40-odd years as a journalist.

A majority of MPs I’ve encountered have at their core a sense of decency and duty to their constituents and country. It can be hard to get at past their egos, which most of them have in spades, especially once they climb the ministerial ladder, but it’s there all the same.

But I couldn’t detect decency in Mandelson. He came across as calculating, insincere, self-obsessed and unshakeably convinced that he was right about everything.

Even by the standards of the most egotistical politicians I’ve met - Prime Ministers among them - he was miles out in front when it came to self-regard.

And he was brazen about it. There wasn’t the slightest attempt to hide it, or put up even the pretence of modesty. He was always the cleverest man in the room, and made sure you knew about it.

He also made sure those around him knew their place. In Mandelson’s Hartlepool constituency, his aides appeared to me to be walking on eggshells all the time for fear of getting on the wrong side of him, laughing nervously when he laughed and cringing when he occasionally glared in displeasure.

Mandelson played on that Jekyll and Hyde quality to keep people off balance and I think relished the uncertainty it fostered in them.

I’ve found something to like – or at least respect – in every senior politician I’ve talked to. Except Mandelson. I found him repellent. That impression was immediate when I met him a couple of weeks before the 1997 election, to write a profile for The Yorkshire Post.

His agent had repeatedly refused to schedule an interview, so I just turned up on Mandelson’s doorstep in Hartlepool, where he’d been the MP since 1992, which annoyed the hell out of him.

Mandelson had already been dubbed the Prince of Darkness by the press for his intimidating attitude towards political opponents – and rivals within Labour – and I got the full blast. He refused to shake hands, disparaged my newspaper and flounced away, declaring he would not talk to me.

That’s when I saw the control freakery in him. Because the encounter wasn’t on his terms, he was furious. Eventually, after several hours of badgering him, his mastery of public relations asserted itself and he saw intransigence would only result in an unflattering profile. So he relented, we talked and he got a fair hearing in print.

Fast forward to 2001 and I went to Hartlepool again for a scheduled sit-down. Four years before, I’d got Mr Hyde. Now it was Dr Jekyll.

Mandelson was all twinkly charm, shook hands warmly and said it was delightful to see me again, which I didn’t believe for a second.

It was all about throwing the person in front of him off balance. I’d been expecting another hostile reception, and it did wrong-foot me when I got the opposite.

He was full of himself that day, the ego off the scale, but in fairness forthcoming and insightful about Labour’s first four years in office since Tony Blair’s landslide and the challenges that lay ahead in his government’s probable second term.

But the more Mandelson turned on the charm, the less I trusted him. When I looked him in the eye, I never saw any sincerity. There was something shielded about him, a sense that he was projecting a persona and what lay behind was inscrutable.

We all know now at least some of what lay behind the façade.

Which makes me wonder why Sir Keir Starmer ever put his faith in Peter Mandelson to be Britain’s top diplomat, as ambassador to the United States, especially knowing of his friendship with as evil a figure as the convicted child sex abuser Jeffrey Epstein.

How was it possible for such an intelligent person as the Prime Minister not to have seen what I saw in Mandelson – the untrustworthiness, the self-aggrandisement, the sheer unlikeability of the man?

He can twist and turn all he likes, and apologise at every public appearance, but if Sir Keir could not accurately assess the character he was entrusting with the country’s most important overseas posting, those who question his judgement are absolutely right to do so.