Honest are almost entirely gluten free, the only thing that isn't is the bread bun they use as standard for burgers however they do gluten free buns too so you don't have to make do with a naked burger. Also breakfast granola isn't gluten free but that is literally all that isn't gluten free.
They have a large variety of burgers, all of which are gluten free, even the special southern style chicken on they have occasionally is gluten free. Each store has their own signature burger too and again, all totally gluten free as long as you ask for a gluten free bun!
You don't even have to worry about the fryers, everything in them is gluten free including the onion rings which are done with cornflour!
Despite the busy-ness they were pretty fast at getting the food out, with the onion rings arriving first, and they were absolutely humongous! Again I had to check they were gluten free, with the waiter laughing (probably because of how many times I checked), he said yes they are definitely fine. And they were so good!
The burger was super succulent and very tasty, with the bun you'd be hard pressed to tell it was gluten free bread, and thee chips were to die for. In all honesty the chips looked bitty and old but they tasted amazing, the skins were still on giving them the more rustic look and they tasted fresh and had a beautiful seasoning, so don't always go off the looks of a dish!
Overall, not the cheapest, about £30 for two of us for burgers, sides and drink, not the worst but also not the cheapest, however I have come to expect London is more expensive anyway. However the food is worth the price, especially as a treat, all the food was so mouthwateringly good, I will certainly be returning whether to this branch or another!