Thanks for everyone's help. Thank you @DavidM and the very helpful Mod Neil who I spoke to on Monday.
Cap removed and extra 6-7Mbps which, while not much, is definitely appreciated.
Also got me onto a new 12m retention contract at a very good price saving me a few hundred £ so many thanks.
Far and away the best service I've had from BT - having had the runaround on chat and the phone recently and being forced to resort to emailing the Chief Executive 18 months ago due to lack of ownership and escalation in the core customer service teams.