Actually I have two new favorite spots in London.
The first one I discovered two days ago, a co-working space with a “free” cafe area for the nomadic folk: the Coffice which offers a buffet lunch for a reasonable price, and I may sit on my laptop as long as I wish. The downside is that my time is limited; lunch is cleared away around 15:30 and the place closes at 17:30.
So because I like to work into the evening hours, I was forced to discover the Ace Hotel right down the street, with their massive open lobby/bar/cafe/common area with a hundred or so folks occupying the cozy tables and chairs, hard at work on dates with their laptops.
I believe it’s open 24 hours as well. I wish I’d discovered this one earlier.