For you 'Doctor Who' fans among my readership (and you know who you are), he played a Corporal in "The War Machines", Ankh in "Underworld", and Skart in "The Power Of Kroll".
Many of the characters he played throughout his career went unnamed - small supporting roles that probably didn't even remain long in a scene. But of course, that's a boon for the Toobworld Dynamic because we can suggest that those characters could possibly be combined into one character and thus link those shows together. (All theoretical, of course.)
In the early '70's, Mr. Jarvis played policemen in episodes from four different series, and it's possible that they could all be the same man - if they all took place in the London area. I haven't seen any of them - at least, I don't think the 'Callan' episode fell into the Netflix mix I watched earlier this year - so I can't say with any certainty that it can be established that all of them are the same man.
Here are those four TV episodes:
"And Mother Makes Five"
Where Our Caravan Is Resting (1 May 1974) - Policeman
Episode #1.4 (16 August 1973) - Policeman
"And Mother Makes Three"
The Eve of the Day (6 June 1973) - Policeman
I Never Wanted the Job (19 April 1972) - Detective Constable
I'd like to think that they're all one and the same man; it would make Mr. Jarvis' role a contender for the TV Crossover Hall Of Fame.
I'm not too familiar with the rank designations in the British police force, so I don't know if Detective Constables could also be lumped into the general category of "policemen". This might have caused a bit of a Zonk, since that episode of 'Callan' appeared first. But we could splain it away with a demotion on the part of Mr. Jarvis' Detective Constable for something that happened after the episode aired, but before his appearance in 'And Mother Makes Three'.
Then again, considering how violent things could get in 'Callan', that Detective Constable may not have lived to see a crossover into any other show. Even if that happened, we could still make the claim that the policeman played by Frank Jarvis in those other shows was the twin brother of the Detective Constable. And that he joined the force in his late brother's memory.
I was tempted to throw in the Corporal he played in that 'Doctor Who' story "The War Machines". As that was about half a dozen years before the 'Callan' episode, it could be that the Corporal cashiered out of military service and then joined the police force. (However, this being 'Doctor Who', the Corporal may have died after urging Sir Charles to flee before the onslaught of the War Machine. I'm not fully conversant on that storyline.)
Again, I haven't seen any of these episodes so I can't make any definitive declaration about my theories.
It may not be the best of legacies - Who am I kidding? It's definitely not! - but it would make for a nice, if small, tip of the hat to the man.....