If you still have 12 months on your contract you would face a quite high early termination charge if you want to go for a cheaper deal.
My bill is similar to yours - for around 60mbps. I bet, like me, you were upsold Halo 3 at some point, with me it was when I was offered an upgrade from ADSL to VDSL FTTC, and Halo 3 was all that was offered to me.
I've since found that I could get the same FTTC speed for around half the price (it's what is typically offered to new customers), but BT are very reluctant to offer it when renewal of the 2 yr contracts become due, especially if you want to renew the easy way on the internet.
At the last renewal I stuck with Halo 3 because I couldn't face the hassle of grappling with BT's agents on the phone, which appears to be the only way to negotiate a cheaper price.
What's more, going by some reports on this community, the agents often get it wrong, even in some cases leading to a complete loss of service for a while, or they upsell you to maximise their commission.