Hotels are the staple diet and the most popular venue for events. London has a huge stock of them to suit any event.
Most 4 and 5 star London hotels have dedicated event spaces with top of the range technology, in-house service teams on tap and fabulous food. If you've got overseas visitors then having rooms available can ease a lot of pain when organising your event.
As always with London, you need to book early. London has the highest occupancy rate for beds in the world so if you want that top hotel, in a top location, with top of the range event spec then they're certainly there in abundance but you need to be quick and book that hotel venue.