I've seen May doing it, but then she's in a slightly different position and probably doesn't get a choice in the matter. Other than that it's only been Farage and Tommeh who have been doing it recently that I've seen.
It has amused me the people claiming this is the start of a slippery slope toward political violence. I would argue it's more in with the British tradition of politicians having eggs thrown at them, which has been around for decades.
It also shows quite how whiny many on the political right...