Defender 200tdi oil light on

Ok weird this yesterday i checked oil level all ok, on the way home pressure light was flickering at idle. This morning checked level all was ok and this morning a 10 minute drive produced from on at idle to on most of the time.
Engine does not appear to be noisy and there is oil i had not noticed before around the Oil Filter, but not excessive, i cleaned and had a look with the engine running and could not see any leaks,but no pressure, oil level still ok though.
No fuel in oil and no overheating, i am guessing as the light flickers the switch is ok??
I am also guessing, oil pump, Pressure release valve, any thing you think i should check, dare not drive it. All happened so fast.

Regards

David

you cant drive it till you know whats wrong switch could be duffit happens or pressure could be low ,it needs checking to see what pressure is cold and as it warms ,favourite cause would be shell bearings though there are other