[leonhandreke]

> It was clear when I travelled back from Marseille that many passengers hadn't realised they would be required to leave the train at the northern city of Lille for passport checks.

When I travelled to/from Romania by train two years ago, border control officers got on the stop before the border, walked through the train to check passports and got off at the next stop, probably taking the next train back. This happened both going into Romania and going back into Hungary.

So, the UK probably wouldn't even have to join Schengen to make this a less painful process.

[sasvari]

It also works travelling from Russia to Finland: Russian boarder guards hop on and check you leaving the country, and then Finnish boarder guards do the same for entering Finland/EU/Schengen. It's not rocket science at all.

[WildUtah]

"the UK probably wouldn't even have to join Schengen to make this a less painful process."

Joining Schengen and getting UK immigration boffins to board the trains and operate efficiently have exactly the same problem: they would require competent leadership from 10 Downing Street.