Not including his stint with Poole Hancock rode 18 seasons in Britain, which I think puts him level with Hans Nielsen in terms of time spent in the British League. Nielsen quit the UK when he was 35, Hancock when he was 37 (or thereabouts). I don't think you'll find anyone claiming that Hans owes the UK anything, who did much the same and rode his final years in Europe. Forgive me if my stats or memory has let me down - I've taken them from Wikipedia but it seems about right.
The main difference is that Hancock has carried on riding at the top level long past the usual, and perhaps by his mid thirties felt he didn't want or need to chase around Europe every day of the week unless the money was silly, which it isn't going to be in the UK. He certainly isn't the only one to make that decision
I will admit being a Cradley fan of a certain vintage makes me probably a little biased