Had already taken all 4 vanos solenoids out and cleaned them.
Although the code was for the exhaust of bank 1, both exhaust solenoids were fairly clean however both intake solenoids were half clogged with debris (picture of 1 below, both were the same).
I'm having the rod bearings changed next week, will put some liqui moly in before the oil + filter are changed to see if the code is due to dirty oil. Although the car has had oil services regularly throughout its life and looking down the oil filler cap looks clean enough.
Due to the code coming up so intermittently I assumed (never assume) that it wouldn't be a solenoid fault as surely the fault would return every time I drive but I've realised this isn't based on any actual knowledge so, I'll switch the exhaust solenoids over and see if the code changes side if/when it next pops up.
Harry