Oil Pressure Low Warning

I am currently looking to sell my 12 Plate Insignia - 160,000 miles

However I am getting a "Oil Pressure Low Stop engine" warning message come up. But when it does come up it only ever comes up first thing in the morning when I first try starting it.

When I stop the engine and restart it, it will then be fine for the rest of the day, Its just that first time in the day. But it wont be all the time, some times it will start first thing in the morning without the message coming up.

It has recently had a oil & oil filter change and it has made no difference.

Any ideas ?