Being (very) `old school' I thought I would check the plugs at 17k miles on my Signum 2.2 `Direct' facelift model - Nov 2005 build.
I was concerned that disconnecting the wiring loom plug on the ignition module that sits above the plugs might upset the CanBus .....
However, you do not actually need to remove the loom plug, as I found out.
So ..... gently pull the long ignition module cover from the space between the camshafts. There are 3 pairs of claw type plastic retainers, and it is just a case of gently working the cover upwards using your fingers.
This will expose the ignition module, which is retained by 4 hex headed bolts
(10mm head size ) - unscrew these *.
Gently pull the ignition module upwards by hand, working along the module from the offside end. The resistance will be `rubbery' as you are pulling the spark plug boots from the spark plug electrical 'nipple'. The spark plug boots are flexible from half way down, so gently pull pull the module up, tilting it up at the car offside end, and carefully lay it to one side.
You can now remove the spark plugs for inspection - mine were BERU 14FGR-8DQU7and seemed fine. However, they did `squeak' for the first quarter turn as I unscrewed tham, so I put a little WD 40 on the threads when I put them back in - just snug them up. If you do use a torque wrench de-rate the torque setting if you do lubricate the threads. (30-50 % ??). I prefer to rely on `feel' for threads in alloy myself !
(* As a postscript, there is a copper earthing bar connected to the windscreen side/near side) ignition module retaining bolt. I suspect this is for screening, but if you are concerned, loosen the bolt, leave it in place in the ignition module, and use a length of electrical wire and croc clips to earth it down to the body or engine. I didn't bother though)
Hope this helps.