I was getting throughput of 5+ Meg on O2 with exact same set-up (apart from the router) so not sure why same cannot be archived on plusnet.
Output from site - http://www.dslchecker.bt.com/adsl/adslchecker.welcome.
Telephone Number 01484xxxxxx on Exchange HUDDERSFIELD is served by Cabinet 13
Downstream Line Rate(Mbps)
Upstream Line Rate(Mbps)
WBC ADSL 2+ Up to 11 -- 9.5 to 12.5 Available
WBC ADSL 2+ Annex M Up to 11 Up to 1 9.5 to 12.5 Available
ADSL Max Up to 5 -- 3.5 to 7.5 Available
WBC Fixed Rate 2 -- -- Available
Fixed Rate 2 -- -- Available