I know it is a bit late, but the two Monarch aircraft that were based at BHX in early April was G-MARA and G-OZBI, however G-OZBI was replaced by G-OZBE around this time.
G-MARA operating the charters, while G-OZBI was operating the scheduled routes.
The two Monarch aircraft currently based at BHX are G-MARA and
G-OZBE.
Monarch are a brill airline and I would reccomend them to anyone!!