I ate out at two tres posh restaurants this weekend - and both had a lot of things that were gluten-free on their menu... the first was Chez Kristof in Hammersmith, where I had three courses of really good food. I had mentioned when I booked the table that I had allergies and quite soon after we sat down a waitress came over and asked me about it and then told me what I could and couldn't have on the menu, which was helpful - avoided the normal delay of having to ask if something is OK then waiting for them to find out from the kitchen...
I had a really good roasted butternut squash, goats' cheese and pine nut salad to start with, followed by mussels and chips, then a poached pear with cinnamon ice cream - the only mistake they made was that the ice cream came in a brandy snap basket (I didn't actually ask if it had flour in, but as they 99% do I avoided it...). Was really good food and is a cool place.
On Saturday night, I went to Alloro - a swanky Italian in Mayfair. Again, the waiter was really attentive and we got a different amuse bouche than the table next to us, which I presumed was to cater for me, which was nice - especially as they didn't mention it or make a fuss... (we had delicious asparagus with pesto rather than a mini fishcake) I then had baby mozzarella and 'aubergine caviar' (which was huge!), then roasted sea bream with braised fennel. For pudding I had creme brulee.
Both places were really nice and it seemed like they really made an effort to make sure I was catered for, but without making a big song and dance about it. If you fancy a swankadero meal, or are celebrating something, I'd definitely recommend either of these...