Many thanks Len. I am pretty sure this marriage was bigamous, as Isabella Punch (nee Robinson) died in 1929, and I can't find any trace of a divorce. Robert Punch (and his "wife" Sarah Watson) described themselves as widow/er which is patently not the case. Interestingly, Roberts son by Isabella was a leading solicitor in the town of Middlesbrough, so I wonder what he thought of the episode. Is that perhaps why they fled to the Isle of Man? Is the island outside English jurisdiction - I guess so!
Anyone else got any ideas?