Its a question that is often asked, without doubt barbel respond well to higher river temperatures so very large barbel are a thing of our times, the warmer the river, they longer the feeding periods, so they are getting bigger.
Richard Walker once was asked what constituted a carp angler, his reply basically said that anyone who fishes regularly fishes carp is a carp angler, he should be not be judged on the size of carp he catches, , as it depends on the water he fishes.
My old friend Fred Crouch (RIP) probably caught fewer double figure barbel and much smaller barbel in his life than someone who regularly fishes Cromwell weir on the tidal Trent in a year, but Fred just loved catching any barbel and was a passionate barbel angler, barbel swam through his veins, he loved all barbel, he was a true barbel specialist who relished fully understanding the barbel in all its complexities, his approach was basic but his knowledge of the barbel was supreme.
I have fished for various species over the 55 years as an angler and up until about 7 years ago I had never had a 30lb carp, I joined a syndicate and after two years I had caught 27 twenties and 3 thirties to 33lb 3 oz and numerous upper doubles, had a i suddenly morphed into a super carp angler? er...no.
The water I was fishing was heavily stocked with big carp, a bad result was a 15 pounder, every year the place was netted and anything under 10 pound was taken out and buried in a trench.
So its all about the river you fish, you can't compare the Swale to the tidal Trent, well at the moment you cant compare any river to the tidal Trent, in essence you can only catch what is in front of you.
Its tragic however how the weekly papers cant seem to judge barbel captures and will choose a 16 pound Trent barbel as being more worthy than a 14 pounder from the Middle Severn or Kennet, yesthe Trent fish is bigger, but the significance of the Severn or Kennet fish is greater.
So to conclude, I think it's about the river you fish, and to me a ten pounder will always be a worthy barbel, and in essence that could be from any river.