No 1 Traveller at Gatwick is £30 for walk-ups, again for a 2 hour slot.
However, not many pay that - Priority Pass, Lounge Club and various 2-4-1 and Groupon-style deals mean that only a minority pay the full price.
I expect similar with Plaza Premium especially as they don't have name recognition in Europe. It would be a result if they go with Priority Pass especially as the current option - United Club - is on the B concourse.
It is still due to open in July I think so we will see ....