SAR - LHR is the northern base in BA! If you get offered DEP LH commuting from oop north is very do-able, but expect to use local B&Bs on occasion, particularly when junior as back-to-back trips are fairly common.
Commuting on shorthaul is a bigger pain in the backside. As a junior F/O your best bet would be to live reasonably close to the likes of MAN/NEW/LBA/GLA/EDI as the domestic shuttles with a staff ticket are the best way of getting to and from LHR for crews who live up there and commute down. Again you would need a regular crash pad near Heathrow or a good deal with a B&B to make it work. There are plenty of Northern commuters in BA, so it shouldn't be too much of a problem.
Thank you very much BMRR for the considered response.