JaJaBinx, I believe that LHR is not yet fully crewed. DEC's have only recently been placed there, and the group are looking to put a third aircraft into LHR.
Ropey Pilot is correct in what he says, and I'm sorry about his lack of weekends at home. However, If you are looking to join bmir to be based at LHR I would say that:
Whilst basing is never a sure thing and we all take our chances when joining a new airline, LHR will require more crews once the third aircraft is placed there;
Whilst the embraers are only there on a temporary basis, they have been there temporarily for over a year now and are likely to remain there temporarily for the next three years if not for as long as it takes for them to become permanent;
People can only give advice based on their own experience. I'm no different, and whilst I have heard of many in bmir that have not been happy with the lack of weekends off, I can only say that in my experience I have not been short of weekends off;
Lastly, and sorry to go on, bmir is still trying to expand the fleet, and whilst in the interim current crews are being sent to other bases whilst training of new crews is taking place, you will be joining an expanding airline.