Sorry - I did mean immigration and not customs (won't have anything to declare so hopefully won't get stuck in there at all). I also will only have hand luggage (was meant to state in the first post - obviously forgot!).

I know once I get to the immigration checkpoint all they will do is spend a couple of seconds checking my passport and wave me straight through - but as the entire EU is one checkpoint I was worried there may be long queues. Though Saturday evening being quiet makes sense - so I think I'll risk getting the first train. If needs be I can run for it! Thanks for the help.

EDIT: I was just reading the Gatwick website and it mentioned it has gates for "epassports". I didn't notice it last time I arrived at Gatwick (though I wasn't aware they existed then so didn't look!) - but are they easy to find/quicker to get through than normal security?