I would say probably more than 50% as the old PH was a cheap rifle bought for many keepers by the estate owner. Nowt wrong with a PH all tended to have very good barrels even if the actions were a bit rattly and they were initially made on the BSA site (ie Birmingham Small Arms) who made a lot of good serviceable guns and rifles. I used one in a professional capacity for many years.
Personal choice only but I would rather have a Parker Hale than a Savage even though the new Savage rifles are now far better than some of the old models. Parker Hale had quite a good reputation for producing decent barrels and good accuracy in their day and the couple that I owned certainly proved that but we have to remember that Parker Hale closed a long time ago and that condition needs to be taken into account when comparing an old rifle with a new one. Nearly all newly produced rifles will shoot with an acceptable degree of accuracy.
Going back to the original question while Parker Hale rifles may have accounted for a fair few deer over the years I'm sure that there are many makes of rifle that have accounted for a great deal more throughout the world e.g. Winchester, Remington, Sako, Mauser, and even Enfields throughout the commonwealth.
When I was starting out every 'keeper and Stalker I knew had a PH .243, .270 or .308 with a Pecar scope, a Brno .22lr, often with a Nikko Sterling scope and either a Baikal or AYA Yeoman shotgun. There were also a few BSA CF2's about. Guests generally had Mannlichers. I remember seeing my first synthetic stock on a Mannlicher Professional and had to have one, it was a long time coming on YTS wages but I bought one soon after getting my first full time job. I must be one of the few stalkers of my generation that has never owned a PH.
Ok I probably should have said within the UK but the answers are coming back pretty much as I thought they might especially from those of us not in the first flush of youth. The comment about Nikko Sterling scopes is relevant too, My first PH had one and it was trouble free. 4x magnification and perfectly adequate.
My first rifle was a PH l had it years and shot a lot of deer with it, it never let me down and l felt 100% confident using it, if mines anything to go by l bet there's many a deer been taken with one, also topped of with a gold crown 6x, happy days we all gotta start somewhere and l for one am happy to have started that way
Love my P/H .243 shot my first Fallow n 2nd Red and first rifle shot fox with it ,only 200 quid and bomb proof .Price isnt always right does the job and didnt need a bank loan or kidney selling to buy it