The oil light in my Mondeo 53 has suddenly started showing, on and off with very little consistency and no apparent common condition that activates it. I had suspected lower environmental temperatures might be the cause but further monitoring has suggested not. There is no pattern to it, cold engine or warm engine, day or night, it varies regularity and length of time lit. Any suggestions would be much appreciated. 

I take it you have done the obvious and checked the actual oil level, with a cold engine and on level ground.

Sorry, yes. I should have stated that. It is full. Possibly over full if anything. It is due a service and I'd planned that for January but I'd doubt it's oil viscosity given that it's last 2 owners were both Ford mechanics that would have changed it regularly. I've owned it since February.