ISTR the TM had M&P markings though
Scratch that, I've seen it with both! Probably depends on when it was made.
That would in fact answer the question. If it is in fact the TM then it should say Made in Japan, Tokyo Marui, ASGK
Can you get a close up of the right hand side of the gun? What do the markings just behind the mag release say?
Any idea roughly how old it is?
Looks like it might be an old JG/Golden Eagle M4SS
Assuming it works OK you might get £75-100 for it.
For something like a DMR where you want super fast trigger response on Semi then yes, precocking does make a difference. On an MP5? Probably pointless.
Part of the briefing at The Mall was always pointing out that Thames Valley ARU were stationed just over the road so NOT using a gun bag was strongly discouraged!
I inherited a Royal Enfield pushbike from my Dad YEEEEEEEARS ago. Had rod brakes and everything.
But yes, BSA did indeed start off making guns. Lots of guns. https://www.bsacompany.co.uk/history/