As long as I can remember, bmi/British Midland have been doing charter work.
In the early-90's there were four dedicated 737's doing charter work, based in EMA,GLA,BFS and LTN, plus the 'nines flying ex-GLA,BFS,DUB on sat night/sun morning to PMI/IBZ etc.
LHR has had a large weekend charter programme for a long while.
Nothing new in this work.