No.4 MkI can be fired form half cock

[Towarzysz_Beagle]

When you say "a good cleaning" did that involve disassembly ?

No.

By good cleaning I meant, removed the bolt, removed the magazine, took forend off and gave it all a thorough cleaning removing all kinds of accumulated crud.

I did not disassemble the bolt past removing it from the rifle. Nor did I disassemble any part of the sear mechanism.

Edit: Just for clarity, I did not perform any function check on the half cock before this point. So this is the first time I've checked it's function. This issue could have existed before I picked up the rifle.