I'm inclined to agree with Thunderbox on this and knowing a bit about the contract/procurement system. The ROF's don't have to run at a profit of course but if their contract is to make 1,000 new rifles, then they make 1,000 new rifles. If there's an over-run say, of 200 rifles worth of parts then they're stuck with them so the obvious thing to do is number them up, make them into complete rifles and send them back to Ordnance. Not as new, but as part of the refurbished/FTR rifles programme they've been involved in.
I know from the big Ordnance depots factory FTR programmes that we were involved in at 40 Base Workshops that we'd get in, say 600 rifles and 150 would be rusted out heaps of tat so Ordnance would get back 450 'brand new' FTR'd rifles back plus paperwork from the R+I office to account for the destruction of the remaining 150. That paperwork would probably go straight into the bin
Likewise at the big Ord factory. 1,000 come in for FTR, 300 are destroyed as worthless scrap, add in the over production and a) you've got rid of the overproduction b) the MoS are happy with your output figures c) now everyone can concentrate on the forthcoming L1A1 rifle and L2A3 SMG project - except that they didn't!
The barrels that were left over formed the spare parts pool for the rest of the life of the rifle - they all seemed to be F55 up until I saw the last new ones a couple of years ago. And the remaining accountable 'master component' mk2 bodies, that couldn't be sent to Ordnance because the body was NEVER available as a spare part don't forget (no they never were, regardless of what anyone has told you....... The number in the parts list is just a part number and a list of parts. Not a list of AVAILABLE parts), went to Enfield to be resurrected as the new build L39.
You realise of course that when the new L42 was first mooted, it was going to be based on a 'new build' Mk2 rifle and body based on the stock piles of Mk2 Fazakerley bodies. However, while the idea was good, it wasn't that simple in practice and it was even LESS simple once the accountants had done the sums! Bless 'em..........