As far as I can tell, the only trick is that Fibre 1 goes up to £36.99 at the end of the 24 month contract term, 'essential' goes up to £32.99 - if you don't renegotiate another term. I guess they'll hope you 'forget'...
Go for Fibre 1 and get the reward card, it's the equivalent of another couple of quid a month off.
>>> BTFibre 2 FTTC