Lauren Frayer

But it's unclear how the British government can police that.

Lauren Fryer, NPR News, London.

It's called an electronic travel authorization, or ETA.

Tourists and business travelers who hold passports from the U.S.

and more than 80 other countries won't be allowed to enter the U.K.

without one.

British and Irish citizens are exempt, as are foreigners with U.K.

work visas or residency.

An ETA costs about $20, half the price of the permit required for many foreigners entering the U.S.

Around 2 a.m., a cab pulled up outside Mandelson's North London home.

And the former ambassador got out.

Police say he was released on bail pending further investigation.

Mandelson is also a former MP and government minister, accused of passing government secrets to Jeffrey Epstein.

The latest DOJ files reveal Mandelson apparently forwarded market-sensitive documents to Epstein to share with bankers.

and advised an American CEO to threaten one of Mandelson's fellow cabinet ministers.

He's apologized for ties to Epstein, but has not commented on these latest allegations.

Mandelson's arrest comes days after that of King Charles' brother Andrew on similar grounds.

Neither man has been charged.

Lauren Frayer, NPR News, London.

Footage shows Peter Mandelson being led out of his North London home by plainclothes officers.