The Engineer in Primrose Hill is a favorite of mine, especially when it's summer and you can sit in the beautifully tended garden at the back.
I'd recommend it because of a strong gluten friendly menu, and knowledgeable and helpful staff, who are happy to cater to your needs.
I adore the vegetarian dish of crispy polenta with grilled vegetables and goats cheese. It has a bit of a chilli oil kick and is one of those perfect dishes where you could feed it to a meat and wheat eater and they'd be completely content. So all you (very brave) gluten free vegetarians out there, this is one to try.
The cheese burgers are also top notch- and I recently discover, 100% gluten free, always a treat, who needs a bun anyway?
If you fancy somewhere for brunch on the weekend and are sick of having nothing to mop up soft poached egg yolks with (is that just me?), then the added sauted potatoes with their eggs benedict/florentine/royale will be a welcome treat.
Next stop is getting in gluten free beer in bottles so be able to sit in the sunshine with..... I'm working on it - watch this space!