You're not getting throttled on any of the TBB speedtest ports?
I didn't try it tonight but I did last night and it gave the same 10Mb result. Anyway I'm back up to 37Mb+ now, so I don't know whether it sped up again at 11pm, I've been watching the telly! None of this is explained by Plusnet's published traffic shaping.
Kevin
plusnet Value Fibre
Using OpenDNS