What appears to be the best plug key for these is the Laser 3682.
It's 250mm long, 3/8 drive magnetic plug socket that fits perfectly down the small holes the plugs are fitted.
Anything fatter and shorter just won't fit and as it's magnetic, you won't have trouble fishing them out of the holes after.
You also need to think about the clip on the air intake hose from the airbox/engine cover (front left of the engine cover).
It's a funny R Clip clamp that squeezes together and hooks over a bump/nipple.
They can be flicked open with a screwdriver, but you'll need to either replace it with a large jubilee clip or if you're refitting it, you need some R Clip pliers (around £5).