Nathan,
Thanks for joining the site, and yes I did know your father, I seem to remember he was ex Army like me, albeit we formed Cambridgeshire Police Firearms unit at the same time and took loads of advice from the Met, as ALL UK Police Forces had to. In those days, we had to conform to Home Office guidelines on the selection/replacement of a Police Marksmans rifle which ended up being the Enforcer.
This was to rationalise and ensure ALL UK Police Forces who had such a wide and diverse armoury of .303's Lee Enfield weapons and other bits and pieces at the time, all conformed, thus singing supposedely off the same song sheet.
The Met & Devon & Cornwall then formed the first Marksman courses. I met them regularly at Lippets Hill and Barton Road, Cambridge for evaluation of the rifle and shotguns and pistols, as we moved away from the S&W .38 to 9mm etc.
It was really a bringing together of minds to try in part to conform to the BritishArmy and the rounds available at the time IMHO.
Sadly, I can't remember too much about your Dad as you meet lots of lads and lasses over the period, and the Met was the biggest and remain so today. with a renaming of SO19 formed in the 70's/80's to what it is today, SCO19 with Counter Terrorism CT-SFO and Armed Response Units as well. So its a big setup for the Capital.
It may be worth you contacting the resident Inspector of the unit by letter, saying who you are, and I am sure they will find other images of him in team shots or on the range days!! The Firearms Training Team are now based in Gravesend, so a call to New Scotland Yard will put you through or give you the address to write to.
Many Police units around the world, followed this lead of having Enforcers and also took stock of what was a good rifle in the day, complimenting the British Army comparison of the L42A1 rifle.
Like the British Army, when the L42A1 left service, so to did the Enforcer, and Forces started to do what they did in the distant past, and bought what they liked to replace it. That is still present today, varieing from Tikka to Accuracy International etc. so many variations.
You will find lots of information on the Enforcer, and I together with two others on this site hold the lists of serial numbers of those issued to everyone around the world.
I can tell you that the Met were the first to take delivery of 12 Enforcers on the 20th December 1973, a further 21 rifles on the 11th of January 1974 and finally another 12 on the 22nd January 1974, they did buy some singularly after that to........................when in comparison as a small combined Force of Cambridge City/Mid Anglia covering Peterborough, Wisbech, March and the Fen City of Ely we only had 23, but the first task was to centralise ALL "specialist weapons at our HQ, and then came the cull on central budgets to one name and one Force Cambridgeshire Constabulary.
Several Forces had the same pains to go through. Thats what makes the rifle so sought after as not many were issued in total.
Good luck with your search, as the faces on the team these days would have changed hundreds of times, but those that start these units have a special place in history and you may be lucky.
Added: You may find this useful as an update too: SCO19 - British Armed Police