I think there has been a few, one sort of led into the next... without going back to the Prizefighting Era's of Bareknuckle Fighting/Boxing and the Beginning of the Gloved Era, there were a few periods where at least one prominent fighter, carried the Load and/or one or two other Top Men along with them... there was Driscoll & Welsh Jimmy Wilde to Benny Lynch with Kid Lewis & Kid Berg in between, heading onto Len Harvey McAvoy, Mills and Woodcock, the 1st Real Chance at British Bigmen Hopes. leading to Cockell & Turpin then maybe Keenan to McGowan to Cooper followed by Downes to Conti to Benn, Eubank Watson and Collins to JC, Froch and Hatton... and a good few alongside them times, Wells, Boon, Roderick, Charnley, Calderwood and a good few other Top men here & there... after this it becomes well diluted by Sanctioning Bodies and Multiple Weight Divisions. So someone else can bring us to date, but the 20s - 50s was strong and the most exciting Era, owing to TV & Satellite was obviously the Benn, Eubank days.
I guess as far as most champions it would be when the alphabet belts started. But that is really not a good way to view it. But 20s-50s is too long to be a era. Something just occured to me right now..... did UK ever had the best (the number 1 p4p) boxer in the world at any moment ?? No, right ? Well, Fitzsimmons could be if we make a p4p for those days....
Yes, IF there really is such a thing... though Britain gets NO Credit for Fitz, it's that simple. the reason I stated 20s - 50s, from Lewis to Turpin there was a TOP Brit or 3 or more in consideration at nearly any given time during that period... But I did state it must have been the Benn/Eubank Era, because there was NO weekly or monthly Boxing broadcasted in the main like it came to be by the late 60s & 70s. cheers man.
Wilde had been retired for over a decade , when Lynch hit the big time ,that's not an era it's two era's Like wise Lewis; time was the 1920's Berg's the 30's. Harvey was a fine fighter but always found wanting at world level. Woodcock for me was never more than domestic level as was Cockell,imo, Wells was cruelly exposed at top level. Boon was game as a pebble but not world class.Neither was Calderwood. Downes retired in64 Conteh wasn't ranked until 73 these are different era's. To me top men implies world class, and several you named do not qualify for that adjective imo.
I'm not British but its probably the current era if British means people from the United Kingdom. Opposed to people from Australia, New Zealand, Canada, South Africa and Jamaica etc(peoples eligible for the Commonwealth belt) in which case this is a very different discussion. Probably the pre 1910s by the more historical definition of British.