A surprise strike by prison officers says The Guardian.
This is thoroughly illegal - whereas prison officers (workers in uniform, natch) have in the past organised sick outs, this is direct industrial action (and will probably see their Association hammered, pass the hat, comrades). Things must be sharp for prison officers to start considering a strike.
Although they'd been balloted, it looks like they didn't give proper notice of the strike.
This looks like the first strike against the paycut by inflation the government is trying to inflict.