No4 Mk1 Rear Sight ......who manufactured it???

Hi......recently purchased a 1943 Longbranch No4 Mk1*. The rear sight that came with this particular rifle is the Mk1 type. I'm trying to figure out who manufactured it. On the main body of the sight at the top there is stamped F9 and close to it a B. Also on the main body the letter P is stamped and it is inside a circle.....the same P inside the circle is found stamped on the adjusting nut as well on the aperture slide.
I know the sight is not period correct for a Longbranch but just out of curiosity I tried to find out the manufacturer in my books...... no success.
Any help would be great.
Thanks.

I'm not certain about this - my knowledge on post WW2 manufacture stuff is sketchy to say the least, but I think the 'P' denotes ROF Poole. It is sometimes seen on No5 rear sights too. I have always presumed that these were made as replacements.

Thanks Roger....just recently found out they manufactured bayonets for the No5 as well. Are the backsights they manufactured fairly rare?QUOTE=Roger Payne;434642]I'm not certain about this - my knowledge on post WW2 manufacture stuff is sketchy to say the least, but I think the 'P' denotes ROF Poole. It is sometimes seen on No5 rear sights too. I have always presumed that these were made as replacements.[/QUOTE]

I don't think they're exceptionally so. In fact IIRC there's a 'P' marked No5 rear sight on the UK version of that internet auction site at this very moment!

Roger is correct. ROF Poole was used to manufacture spare parts for artillery, (25 pounders especially) naval Ordnance and small arms when needed, as a result of the closing down of orders with the usual commercial contractors. It was really a last ditch effort to keep the old ROF's open and running. A lot of them went on for many years but the inevitable happened - eventually