Well here's a little info that might make your life easier, Chris. Last year whilst I was talking to one of the EA Fisheries Specialists from the Newcastle office he told me of a fish he'd been sent (photograph of) taken from the Tweed to identify, turned out to be a barbel. Small but definitely a barbel.
I'm not sure just which section of the Tweed it was taken from, but if they get established ...
Small numbers of barbel are also now showing on the main Tyne in very isolated areas, and of course they are now well established on the Wear, from the tidal water to above Bishop Auckland. We, DCAC, have a couple of members in Edinburgh who occasionally travel down.
River Wear barbel (so they do exist) Not weighed but taken by DCAC Treasurer Frank Bell on a size 20 whilst roach/dace fishing