It is not that formal scary as it is more "media" and "trendy" than stuffy Brit. On weekday lunchtimes there will be lots of people in suits just because they've come from work, but there will also be men in just shirt/trousers or trouser suits/reasonably smart casual stuff for women. I have worn a black trouser suit every time I've been there, usually because straight from work though. It is one of the less stuffy restaurants I would say, but just no jeans/trainers.
Thanks for that....it's ds I'm worried about as he has a nice shirt, but no formal trousers, and only geox for footwear. I foresee a painful session in M&S trying to squeeze him imto trousers, ot having to drag him to H&M in Brussels before we come back. His school doesn't do uniform, so he doesn't need formal gear yet!