It's FTTN.
I really hope you're right about the weekend being the culprit.
I mean, I can understand congestion lowering my speeds but to such an extent? It's quite depressing, to be honest. 
I'll give it a week and see the behaviour, as I've only had it since Wednesday. That way I guess it will help me determine if it is indeed congestion (as you mentioned) and not a fault.
Thanks for suggesting it DrQwerty90 