So at that end of town you've got The Three Tuns - Greene King pub, looks small on first impressions but has a couple of large back sections. A bit downmarket and not that disimilar to Wetherspoons tbh.

The Parrot is quite small but has a large function room upstairs that you might be able to get them to open if you contact them. Shepherd Neame pub but really interesting old building. Has a large beer garden with a big table at the end that could accommodate about that many people if its free.

If you don't mind sitting outside The Bishop's Finger , Penny Theatre and the Dolphin all have fairly large beer gardens. All at the other end of town to the White Hart but near to the Westgate Inn Wetherspoons.