Upvote:2
There are a lot of similar questions online for Laos, but The WorldTravelGuide tries to index information about this topic, and according to them - if flying in, citizens of Britain or other EU countries require a return ticket.
From sources online it appears that if you get asked, you could say you're continuing on by land travel, but may be asked for evidence of this, and all you'd need is for some pedantic gate agent to cause you problems.
Upvote:2
I was stopped at check-in by Silk Air before leaving Singapore pre pandemic. Was going to come back by train but they said no.