He had little credibility left, especially after it was confirmed he had been hosting parties while expecting the rest of the nation to stay home and not mix.
When you've been denied the chance to be with a family member during their dying moments, only to find out the person leading the government who made the rule was hosting a wine and cheese party, it's easy to see why you'd be angry about it. If anything I'm surprised the politicians here who have been flagrantly breaking their own rules haven't been similarly punished.
Last I heard sterling was up against the dollar so it seems like the market thinks it's a good thing.