Stephen,
Have a read through this thread here. Well, the first post anyway.
The photo referred to is this one here.
Like you I was getting surge on left handers. I took the engine out and measured the line of where the sump was (red line on that picture). I then measured the dipstick high and low oil levels and drew them on (purple & yellow lines).
My theory was that because of the angled install in the Caterham, oil gets trapped above the gasket (Seen on the right hand side in the photo), and for it to get to the pickup, it has to flow up the gasket, drop into the windage tray and then filter down into the sump. I reckoned that it couldn't do this quickly enough during surge. Also, because the small triangular volume of oil below the gasket would flow towards the deeper side of the sump where the capacity is greater (If you know what I mean), it doesn't get up to the pickup in time.
I decided to remove the windage plate and sump gasket and try fitting the sump with silicone sealant. I got no more surge. Happy with this, I then refitted the windage plate (It does combat windage) with the sump gasket cut so it had no deep shelf/lips. I ran the car on the road and track with R888s and never got any more trouble...although previously I had been able to with a decent corner.
As others have said, the best solution is a dry sump, it'll also de-aerate your oil...which can be a problem on wet-sump Ks. I got seriously shot down on that previous thread by the dry sump brigade, mostly for being young and foolish, which I freely confess to being...that said, I fixed my wet sump problems, and none of them did 😬
Its entirely up to you if you want to try it for yourself. I was happy to try it, as it was worth a shot before either toasting my bearings or buying a dry sump, both of which are costly modifications.
Willie