Oil pressure issue???

Discivery 2 '03 v8 bosch Before Xmas I had an occasional oil light come on. I was only doing a mile or 3 journeys so just intended to top up,.this I did before I had a 300 mile round trip. All was fine until right near the end I was on an uphill gradient doing 80ish (yes I know) stuck behind a very slow vehicle and one coming up behind so decided to boot it past and clear out the valves etc.... "yawn", anyway all good for about 4 to 5 seconds then it just seemed to "blow" and oil light came on. Still running bit rough pulled round corner and had lost a litre or 2. Presumably then but possibly some on journey.. drove it slowly home about 12 miles and parked up. 2 weeks later oil level stable no dtc's but still rough and oil light permanently on.
I seem to have oil from bottom rear of ace side rocker going behind the block and behind.
Suggestions? Oil pressure gauge? Pump? Blown rear blank plate? Rocker seal? Head? Any suggestions as to best tests or order to address these. I'm on side if a lane without a workshop so a bit awkward.
Will attempt pocs later when on PC not phone.

hopefully links work:-