As to whether the UK has pulled such operations in the past, there is no indication of an assassination of a former spy or false flagging thereof, but a parallel could possibly be drawn between false flag operations by the UK in coordination with the US during the 1953 Iranian Coup d'etat called in the UK «Operation Boot» and in the US «Operation Ajax». (politics.stackexchange.com)
It's possible that someone else claiming to be affiliated with Anonymous hacked the site, but Anonymous itself seems to suspect the whole thing was a failed false flag operation. (relevantmagazine.com)
Government false flag operation to give the public a reason to accept the government taking all guns away.. (religion.blogs.cnn.com)