Jon, same excuse as for Pedrag! I suspect that the fish you are catching are old fish as Chub do tend to go a bit tadpole like in old age. My mate, who fishes the Wharfe a lot more than me, calls the bigger Chub 'breeze blocks' as thats exactly what they look like - a brick with fins!
One thing that we have noticed is that there are a lot of fish in the 4lb to 5lb bracket that still look relatively young so that bodes well for the chub fishing on the Yorkshire rivers over the next few years,