I would say it was post 1980's Service number two (Mk5 is not correct IMHO) as the kukri of this type tended to be issued with month and year marked on the blade in the 80's;
As in the one on the left, the one in the middle has even earlier markings;
Here is a nice Service number one, from the Gurkha museum in Pokhara, Nepal;
For a fairly detailed history of the Gurkha and the kukri follow the link;
Link