British border staff have faced threats of arrest by Belgian police for trying to stop people exploiting a loophole allowing them to enter the UK without passport checks, the BBC has learned.
Passengers can travel from Brussels to Lille without showing passports as Belgium and France are both within the Schengen area.
But they can then stay on the train to the UK as there are no further checks.
The Home Office confirmed it was working to tackle the "Lille loophole".
http://www.bbc.co.uk/news/uk-16058860