Hi
Just to update you, since reverting back to the old version of the theme the CPU has been perfectly fine (all weekend) with no downtime.
So it 100% links to the theme and the latest woocommerce update as I did update both but then reverted both; so something between both these is causing high CPU usage.
As I am on a live site I could not test one or the other so decided to revert both, however when I did disable the theme the CPU improved immediately so hopefully this helps.
Thanks again 🙂