Rob Watson

This is a seismic moment in British politics.

It's the first ever by-election victory by the Greens, meaning Labour has been beaten by a party to its left.

The strong performance by the anti-immigration Reform Party confirms the threat posed to Britain's main parties from populists of both left and right.

Although the Greens have promised a new kind of hopeful politics, they have been accused of sectarianism with their emphasis on Gaza in areas of the constituency with large Muslim populations.

America is changing, and so is the world. But what's happening in America isn't just a cause of global upheaval. It's also a symptom of disruption that's happening everywhere. I'm Asma Khalid in Washington, D.C. I'm Tristan Redman in London, and this is The Global Story. Every weekday we'll bring you a story from this intersection, where the world and America meet. Listen on BBC.com or wherever you get your podcasts.

Our UK political correspondent is Rob Watson, and he spoke to my colleague Celia Hatton. This is a massive development in British politics. I cannot remember a senior political figure like Lord Peter Mandelson being arrested on the suspicion of criminal offence. I just can't remember anything like it. What has he been arrested for? What has he been questioned over? It's, as you say, it's misconduct in public office. What does that mean in plain English? It means that he was supposed to be doing a job on behalf of the public.

but did something seriously wrong. I mean, specifically, we think it's to do with the time when he was trade minister, so a senior government minister in 2009, after the big financial crash, and that he was passing market-sensitive internal UK government information to his friend Jeffrey Epstein. Give us a little bit more of that context. As we've said, Peter Mandelson has been a public figure here in the UK for years. Remind us how he came to prominence?

He's not some obscure politician that people in the streets of Britain would be saying, Peter who? Not at all. He has been a huge figure really in the last four decades of British politics, partly because he was one of the masterminds of what is known as New Labour. That is the idea of moving the Labour Party more to the right of politics under the leadership of Tony Blair to get it back into office after many years in the wilderness. So he was the architect, one of the architects of the so-called New Labour Project.

He worked for Tony Blair, he was a minister in Gordon Brown's government, he was a commissioner for the European Union, and of course most recently, most controversially, the British ambassador to Washington with the hope that somehow, given his past skills, that he could establish a relationship with Donald Trump.

We've seen the arrest, as we said, of the former prince, Andrew Mountbatten-Windsor, and now Peter Mendelssohn. So we've seen arrests in the UK, but not in the US. No, and of course there is pressure now in the United States from congressmen and others to say, hang on, look at what the Brits are doing. I mean, they've arrested a former prince, they've arrested a former senior government minister. We should be doing more of the same. But I guess it's partly a cultural reason. In the UK we do scandals.

Rather differently here, a passion and relish about seeing the rich and the powerful cut down to size.

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Look at the closing words of the Statement of the King.

And two of them are duty and service.

And they are the foundation stones of the modern monarchy in Britain and, frankly, of the House of Windsor as well, the house that has held the crown for the last hundred or so years in that name.

Now...

What is suggested by the arrest and the investigation, and it is important to remind everybody that former Prince Andrew strenuously denies any financial gain or any sexual impropriety, but what is suggested is...

is that a very senior member of the royal family has done the opposite of duty and service.

And not someone who is caught drunk outside a nightclub throwing up or someone who ends up sleeping with somebody else's wife.

All of this, you know, goes down the decades for the royal family and people understand they have teenage lives and they have difficult family lives like many do.