To answer an earlier question, B1 is mechanically orientated, although these days it does involve a lot more on the avionics side. B2 is avionic (electrical) orientated. There's nothing to stop you gaining both, except a lot of hard work and studying and exams.....to get both. People tend to start off as one and may gain the other later.
There are or were seperate maintenance organisations that offer apprenticeships, not sure these days though, Monarch do, not sure about Thomas Cook etc, Virgin do, no idea about BA (doubt it).
BAMC certainly used skilled people from different areas, vehicle mechanics etc, that is a BA subsiduary in Cardiff.
If all you want to do is work on aircraft, I would try the civil route first rather than the military but that's just my opinion.