Big thanks everyone that commited to this post. Appreciated much, now i had the time to picture the barrel flats and the H prefix serial number on the bottom rib as Dan suggested. It seems that the gun was reproofed in London in 1981. Excited to hear your thoughts! Pictures below, all the best.

Kem

[Linked Image from i.ibb.co]

[Linked Image from i.ibb.co]

[Linked Image from i.ibb.co]

[Linked Image from i.ibb.co]

Awaiting your responses gentlemen, with all respect thank you for helping out.