I've used The Castle in Leicester as a venue, and it was great. That said, they've changed hands and are now https://m.facebook.com/castlecastina/

The previous owners didn't charge a venue fee to use one big room plus the patio, just the cost of food/drinks (admittedly not cheap). No idea what pricing under the new owners looks like, but if they are inviting under 100 people the place itself is wicked awesome.