Faulty spirit level?

[Johnmelad]

I try to get skirting level as it creates a lot of work at external corners if out of level.

 

[pinenot]

Simple, place skirting on both high spots use a shim the depth of the deepest gap and scribe the whole length. Best done this way when the two ends can remain full depth otherwise the scribing will continue round the corner onto the next lengths. However I have never come across anything quite this bad, mostly it can be achieved as I described on the later piece in my last post...pinenot