Right, so I got busy with this last night!
Located the two Vanos solenoids and started by unplugging them taking note of the cable orientation (easy since the cable holder keeps them in the correct order - top going to the top solenoid and bottom to the bottom solenoid etc).
Both solenoids out, not as much oil as I thought would spill out, but then the engine had been not moved since Friday.
Decided to use some unleaded petrol that I have in bottle for cleaning things and it seems to be one of the effective cleaning agents in general. Then once satisfied that all of the gunk had dissolved and been cleaned off (replace with fresh petrol in necessary) and had time to dry properly, I dipped them into some spare oil (as per what the car takes just to play safe) so that any petrol residue is not left.
Two cleaned solenoids - in retrospect they weren't very dirty with the exhaust solenoid being the dirtier of the two.
Unfortunately I can't say that I feel or hear any improvement, and no change to consumption, so I gather they were functioning fine to begin with. But does not hurt to have them nice and clean - and now that I know how to do this it can be cleaned easily in future.
For those wanting to do this, above link is a must, but found this pretty easy!!
Really easy job overall, as you can see nothing had to be removed to access the solenoids. A bit cramped but enough space to work - just take time and care not to drop anything! Ideally use your small 10mm socket to loosen the bolts holding the solenoids onto the head, and then remove them carefully with your fingers. Push metal clips to release the plugs and gently pull away from the solenoids - take note of which plug goes to which solenoid. Place a rag beneath the two solenoids and pull them out - helps to twist them slightly as you do this. Expect a small amount of oil to spill out. But be careful of the plastic ring that can easily slide off the solenoids when removing since you have to angle them out from this tight space, this is because the O-rings tend to stay inside rather than come out with the solenoids. Clean and refitting (only the forward portion with the holes) is as simple as reverse of the above. Oh, only do this when the engine is cold!!!