I have also been with PlusNet of over a year and, like the previous two posts, have found them to be excellent. Telephone support has always been very quick and helpful. No hesitation in recommending them.
They have recently restructured their pricing and I have just ordered a 'regrade' of my present connection speed from 512k with unlimited (Premier) bandwidth at £21.99 p.m. to 1.0Mb capped at 1GB bandwidth per month for which my subscription will be REDUCED to £14.99 p.m. I feel I do not need a large bandwidth at the moment, but if I exceed the 1GB they will just bill me for the excess. If I find I regularly need more than 1GB I can then upgrade again at £1.75 p.m. for each extra 1GB. Have a look at their site click here and see the various 'mixes' of speed and bandwidth that are available. They have also introduced a facility to monitor the bandwidth usage, and they will advise you when you are approaching the included limit you have chosen.