They currently do an 80Mbps down, 20Mbps up service on both fibre-to-the-cabinet (FTTC) and fibre-to-the-premises (FTTP).
When I asked about gigabit (which is available on the BT FTTP platform) - the answer I got gave me the impression they want to make sure their backbone network can deal with that kind of traffic before they launch anything like that.
The other thing they mentioned was that the high-bandwidth services most people use (I guess Netflix and the like) have an upper limit to the data rate -- and it's nowhere near gigabit.
I'm not entirely convinced that the difference between 80Mbps and gigabit would be noticeable on anything but heavily-seeded torrents (e.g. Linux ISOs) or backups being sent to providers with similarly fat pipes. It's a great marketing strapline though, and clearly many customers see the headline "up to a gigabit, only from XYZCo!" and decide based on that.