I think he might be a bit tense. Being at the top with such a slender lead and two draws on the trot can easily make for a squeaky sphincter.
Plus, being a black cab driver in London must have been even more annoying recently with the Ubers and mini-cabs etc. What's your excuse for last night though? When I do something like that (and I've already done the same thing twice this season costing me a 0-5 v Clayton Royals and a 0-7 v the Donks in FL1, it's usually because my mind is elsewhere.