The Pattern 18 used a new system of converting older rifles to .22 by boring out the barrel and soldering in a new .22 liner in a system known as PARKERIFLED. The top of the receiver was stamped "PARKER HALE .303 CUM .22 SYSTEM"
Tony - could you clarify something for me - is the below a contract produced No2 MkIV*? This will not chamber a conveyor, only a .22 round.
It is a 1918 No1 MkIII* converted to .22 by Parker Hale but without the full stamping you detail. On the muzzle picture it appears that there is a sleeve insert within the original barrel, although I believe skennerton says these were made with solid barrels. This rifle is renumbered all over with a two letter= three digit number. My assumption was this was a WWII conversion using a converted barrel
There a a few interesting elements on this rifle - it is a 1918 MkIII* BSA rifle (with slab sided cocking piece) but has the stock marking disc which is an odd discrepancy. It also has a piling swivel.
The spring inside the magazine was removed and the base stamped 22 (last pic). This is a single shot weapon with the magazine simply catching the spent .22 case.