We had a very bad experience when visiting Maxwell's.
My son has food allergies, and we therefore ordered from their gluten free menu. We also informed the staff about the allergies.
The meals tasted OK (gluten free Fajitas and gluten free Fried chicken), but 10 minutes after we left the restaurant, my son had a severe anaphylactic reaction.
As this happened on a Saturday afternoon, this incident ruined our weekend in London.