Small glitch from no driving over the winter...
It is the first time in months it was a reasonable temp. in the garage and I was in the mood to fiddle with the car - so thought I would turn over the engine. It hasn't been started since the beginning of October.
Battery has been on trickle charge for most of the time - spark was good initially, then no oil pressure - needle wasn't even moving & the ECU cut the spark. The dipstick showed oil in the sump - it was still in the engine at least but presumably just drained out of the oil pump.
Googling confirmed by quick advice from RhoCar (first hand knowledge preferred when I can get it): Plugs out - turn over a few times and pressure should come back.
All sorted again - oil pressure back, plugs inspected and back in, a few cranks to get the fuel running through and we are back to normal.