When travelling between France and the UK via the Eurostar train, I have never actually been stopped by customs on either direction. I've seen some people being stopped, but it seems that it's on a somewhat random basis.
I'm considering traveling by coach this time, but I wonder if the customs are more strict, e.g. should I make sure to have receipts for all my electronic equipments (laptop, camera, etc.) and fresh fruit (to prove they were bought within the EU)?
Also, for coaches travelling during the night, is the procedure lenghty? The coach website displays the total travel duration, but not the amount of time one should be "awake" (e.g. waiting for customs or something else), so I wonder if I would be able to sleep during most of the time or if I'll spend, say, one hour waiting for customs clearance, or something like that.
Note: my question is more about the practical situation of a coach-based customs (which I have never actually been through) than the theoretical fact that one should always bring receipts for each valuable item in their luggage.