Severe Lag issues

[#1]

Hi Ladies and Gents,
Seem to have an issue whilst playing xbox/psn online multiplayer, where there is considerable lag and slowness when playing.
Looking at the signal strength (playing Call of Duty Back Ops and other like titles), it shows 1 bar out of 4.
My NAT type is open, I have performed the DMZ function, however the problem still persists.
Any suggestions are welcomed.
Thanks,

[#2]

Maybe you could ask Plusnet to have Interleaving OFF  providing your line Is of good quality and good connection?