As it says..... when the motor is upto temp, on tick over the oil warning light flashes. NOT flickers like low or thin oil, but actually flashes in the same way the coolant light flashes when the coolant level is low.
it doesnt do it all the time, just when it feels like it. plenty of oil there, and its the thicker oil for older cars!

Any clues would be appreciated, cheers!

its a 1.8 4cyl automatic Mk1 golf cabrio 1993

95 Cordoba mtrs at times had a oilflow problem bringing on an alarm and flashing light due to dried oil sludge clogging the filter...may need sump off clean out..

do you get any tappet rattle and lack of lube excessive noises? loss of power?

no noises, no rattles, recent service before i bought the car, when i bought the car it was pumping the oil into the coolant via the heat exchanger, this was replaced and the oil topped up with thicker old car oil.
i've no idea if it was flashing before the troubles.

could be as simple as a loose wire or chfed wire making contact
as its not a newby hay!

Try replacing the oil filter. My mate had a jetta that had a similar problem, good oil levels flashing light. It was a blocked oil filter?