An interesting thread, I,ve been reading up on the Law a bit more than normal recently, (still doesn't make sense) little snippets that I've forgotten or never acknowledged are the bit's that stand out, Peter mentioned the status of a deactivated firearm and is right in saying once its deactivated it is no longer a firearm.... in fact its harder to buy an orange painted air soft than a deac, but thats the way it is.
The SP debate I can't see a problem, the thing is you need to look outside the box, Tankhunter mentioned the fact it was a Semi Auto rifle to start with and from what I was told is a lot to do with the reason we have them, 17 odd years ago L1A1's were advertised in Gunmart for £350 (sec 5).
Ship them rifle's to another country then they are what that country states they are, strip them down and you have a selection of rifle components, (no such thing as a section 5 part) so a foreign country now has a load of rifle parts, build a rifle out of them with a new barrel and do a small conversion on the bolt carrier, then they are a straight pull rifle and
UK legal.
The problem lies with such persons as Roy mentions, I know some "parts" were making there way back to the UK and being re-barreled here I guess everyone was getting on the band wagon.
A lot of straight pulls out there at present, M1 carbines, M1 Garands, AK variations and other
Russian rifles, to top it off we have the famous AR15........ being a previous owner of an AR15 (M4) it was a lovely rifle but in straight pull a real pain..... just my view but was very fussy on ammunition and on a cold day cocking it every round become unbearable, again just my view and the reason I sold it, give me a bolt action rifle any day, quicker to operate and easier..... and more accurate.
The problem I find is when people push there luck..... anyone in the UK would of heard of the lever release 9mm by a UK company famous for AR15's, again a nice piece of kit and it does the job but it stood out like a sore thumb..... and got noticed more for things it wasn't meant to do....
To anyone with the above then I say good luck to them and and enjoy it.....
If your looking at a straight pull then buy off the shelf, if you want a Bren Straight pull then I would do the homework, get some plans, read up on the
USA closed bolt system for the parts kits and start from scratch...... and be prepared for a lot of swarf