This morning (3am - 6am) there was some planned engineering work which made my connection really slow, called tech support and they said it'd be fixed by 7am but my connection is still really slow. The upload speed seems to be ok but the download has died
I've tried connecting directly to the modem and it hasn't improved the situation.
BT Buisiness Tech Support tell me they don't see any faults on their end and my line profile is set to 77Mbit. Any ideas?
You could try ONE power cycle of the modem and a reset of the home hub.
Looks like you are going to have to get back onto BT Business Tech Support and report a fault. It would obviously appear to be connected to what ever the engineering work was.