Plenty of fighting age males. In this case age is actually an advantage to the British, because a lot of their guys are old enough and have enough wisdom to organize and pick their openings, while still being fighting age; whereas these ad-hoc Muslim militias I've seen have no leadership or direction. They just want to scream takbir and kill whitey. This doesn't bode well for a stand up fight, because they will be unable to hold formation, and likely to be picked apart by the superior numbers of British.
If push comes to shove, and the gloves need to come off, I mean really come off, the British can arm themselves with whatever they need to win. Armaments is my least concern.