Venue help please

This is probably a big ask, but here goes anyway... I'm thinking about holding a birthday party for a friend in the summer, but don't have a massive budget. My wife is an excellent cook, and our friends love her food. Does anyone please know of any venues (preferably in the Central London area) that can be hired for an evening, but you can bring your own food (and possibly drinks) into, to save money with exorbitant mark ups etc? Yes, it's a big ask, but any thoughts or advice would be greatly appreciated.