If the first line of the "Featured Products" says "WBC FTTP" then you can apply for the trial at http://trials.plus.net/
Another way is to go to the BT Retail website and see if you can buy Infinity 4 from them (FTTP at 330Mbps download). If you can then you can also apply to join the Plusnet trial or use BT or even Zen (the latter 2 offer FTTP as a product not just a trial)
Finally Plusnet only offer 2 speeds for FTTP, 40Mbps down/2Mbps up or 80Mbps down/20Mbps up. Use BT if you want faster.