You kind of have to take Marmite as a kind of grown up parlour game item - explaining that you really don't expect them to like it.
Otherwise, pehaps a selection box or a couple of packets of classic, "Biscuits for cheese" like Carr's or Jacob's because you could try to incorperate them into, "l'apero" ritual. The best they have in that area are Belin crackers and other boringness.
It's such a shame that we can't take dairy products or meat into the EU anymore, as otherwise I'd have gone to town on Lancashire, Cheshire, Wenslydale, Caerphilly and so on.
The nearest crumbly cheese to all these would probably be Cantal but it's not the same.
They might like pickles or they might not. For reference, the greatest of British culinary horrors that I ever heard of was, "Green vinegar sauce, not pistou, not pesto...Green! vinegar!" Turned out to be mint sauce that my friend was confronted with on a school trip to, "Fucky Stone." (Folkstone)
Tradionally, the French were very averse to anything spicy. "Trop épicé!" but that's changing.
You can't go wrong with sweet stuff although seeing as you said that you wanted to avoid alcohol, if your hosts have any Muslim heritage, watch out for gelatine.
Rhubarb and ginger jam caused quite a sensation once upon a time, Hobnobs, flapjacks and similar might be an instant hit because there's not much of an oat and golden syrup eating culture over here.
Sticky Toffee Pudding might set them raving or might be, "Trop lourd."
Anyway, have a lovely time. It's the thought and gesture that counts. I'll never be convinced that Russian, "Herring in a fur coat" salad is wonderful but it was nice to try.
PS. Whilst you're there, try the full range of Brets Crisps. Chèvre et piment d'espellete is my favourite but obviously you have to try every flavour to find out.