It doesn't mean BT are going to offer it, just that BTWholesale are showing it available.
I don't know of a single ISP offering anything above 330 at the moment (excluding Spectrum in Wales, but they have their own backhaul).
edit: removed incorrect info, thanks to ignitionnet.
OpenReach FTTP PricingUp to 500Mbit/s /165Mbit/s
Install exc VAT £500.00
Annual rental exc VAT £660.00
Up to 1000Mbit/s /220Mbit/s
Install exchange VAT £500.00
Annual rental exchange VAT £960.00
Can't see this being a BT Retail product in the near future.