I recently tried a couple of boxes from Graze. Although they don't yet cater specifically for Coeliacs, this is something they are planning to do in the future. However, you can see a list of all the ingredients by clicking on each product and you can easily fill your boxes with g-f stuff. There are only a few no-nos - mostly the chili-flavoured nuts. You can get fresh fruit, dried fruit and loads of different nuts and seeds etc - and delivery is included in the cost - to anywhere in London.
Lots of fun when it arrives as the packaging is really lovely (and all recyclable) and the combinations of nuts/fruits etc are really imaginative and delicious. When I emailed them to ask about allergy-friendly foods, I got a really lengthy and detailed email in return.
Definitely worth a try!
