Thanks Dipso, it has only been two days since activation (as of Sunday morning). According to BT my line can provide up to 8mbps. I think after 10 days I can contact my ISP and they will take up the speed with BT.
I was hoping for more than half the advertised speed!
I have to say it doesn't appear any different to what it was at 2mbps but I suppose it must be! (at 2mbps I was getting speeds of 1.8 )