New coil pack, plugs and HT leads seem to have sorted the Ka misfire.
Then of course something else goes. There was a tiny coolant leak near the engine so I changed the offending hose, freaking thing was still leaking so I was yanking the hose back off and the sodding spigot cracked off the thermostat housing! Turns out they make them from GRP!
Fortunately we live in such a fucked up world that I was able order a new pattern part from China for £8 and fitted it today. All sorted.