The new Terminal 2 at LHR is still in soft-opening, with more airlines transferring from the old (and doomed) T1, but many lounges, from United Club to Lufthansa's are already opened.
Plaza Premium has had presences in Asia and North America, but has finally landed in Europe. LoungeBuddy has the goods. Looks pretty nice.
They will also open an arrival lounge in the near future.