Uncapped in today's BT Wholesale world is not something that most ISPs can afford to do, unless you are heavily contended or shaped. However, in my experience most people who want unlimited just want a more 'reliable' bill for easier budgeting.
I would suggest trying to find your current use (If you can't or don't know this just let us know what you use the connection for e.g. just email and some web traffic or you run a streaming media and major p2p node from your office
) and then looking at packages (Or making a package in our instance) that fits your needs and budget.