We hired part of the Avalon for my husband's 40th and it was brilliant. Have a DJ as well so really fun for dancing late into the night

http://www.theavalonlondon.com - Clapham South

It might not be big enough, but the County Arms has a separate function room upstairs with its own bar.

Thanks so much for suggestions so far - following up on all of them, and they look great! Please keep any other suggestions coming - I'm discovering many places already booked up in October....perhaps there are some more hidden gems out there!

The Jam tree in Clapham?

I've been to a great party at the Bolingbroke on Northcote road, which the birthday boy had hired entirely. I think it would comfortably accommodate 70-80 guests. Not sure about the financial terms though, I expect they would have a large minimum spend if they close the entire place for you. But it's a great location, and the area at the back makes a good dancefloor.

Also the area in the basement of Del Aziz in Clapham Old Town can be hired privately. Great for dancing.

VdM

Please let me know if you have any great ideas - looking for a venue suitable for around 70-80 for drinks (possibly a bit of dancing later!), ideally a private room or at least separated from main bar area. Will be in October, so outdoor space not likely to work. Anywhere in Clapham, Balham, Wandsworth, Earlsfield etc. I liked the Gallery room at The Exhibit in Balham but sadly already booked on our preferred dates - so anything similar to that would be great. Thanks in advance for your recommendations!