With a hub, you can get as many as you want, but you'll see a fast lack of performance with adding more computers. Don't use a hub unless you have 3 or less computers, roughly.
A router lets you have as many computers as you want, given the money. Most consumer wireless routers let you attach about 4 computers with wired connections, and about 64 or so with wireless connections (though this number may make it a little unreliable).
Also, the 'BT home hub' is, I believe, a router and not a hub in the technical sense.
I can personally recommend Tiscali (pretty cheap too), and then simply get your own wireless router like this one:
http://www.ebuyer.com/UK/product/118010/rb/0