He's best friend's with Mick and Toni is his ex-girlfriend. So, technically, that makes Ketch uncle. It would make sense for the son to call Ketch his uncle.
Not the best image of either but the resemblance can't be denied. Also, it may explain the complexity of Mick and Toni's relationship and why they bicker like a married couple.
UPON FURTHER EXAMINATION OF THE AVAILABLE EVIDENCE, I HAVE COME TO THE CONCLUSION THAT MICK DAVIES IS ACTUALLY THE FATHER OF TONI BEVELL'S SON. EVIDENCE IN THE COMMENTS.