what about the Rainbow Building run by the local charity Charterhouse in Southwark?
Its near Borough tube station and is sizeale, over several floors which would be able for what your talking about.
The Charterhouse building itself nearby is also sizeable and has a small garden (for your drummers?)
The usual line from charterhouse is that Community Group Il Covo use the space for classes for adults, cafe, art workshops etc but nothing of that description actually appears to happen there. You might be ab;e to peruade Charterhouse that the intended function of the Rainbow building as a community space isnt being realised to its full extent and that you should be allowed to do it.
If you can that is, what an undertaking - good luck!
Il Covo do do community events and classes etc in the Rainbow building - keep your eye on the noticeboards at the bottom. They also sometimes leaflet the local estates, but they rely a lot on volunteers and can only do what they can.
As for the building - too right its not being used enough! There are many existing users, especially the youth activities which run most evenings, but there is scope for many more, as long as they can put up with the Victorian ancientness, lack of level access, and difficult spaces that the building has! (dont be too put off - it has good spaces and a great community atmosphere too). Balance for life has now found a site, but Charterhouse would welcome enquiries from others: 020-7357-7733.
A refurb is essential in order to make the building suitable for the huge variety of potential uses it could have, but it is a difficult job for an independent small charity to raise the money for this. I am a trustee of Charterhouse and have hopes and visions of a thriving, open building with heaps of activities, a cafe, arts, etc etc, and am doing my best, but its a big and slow project to refurb a building of this size - we are talking several million pounds. We have lots of small community halls in this area which are often also under-used, but Charterhouse is our best hope for a fantastic community facility for all locals.