Such an easy job made so bloody difficult by Peugeot! I am, of course, referring to the plastic panels. The two in the wheel arches and the undertray. And then I couldn't find my stash of zip ties to replace the broken bolts so my undertray's now held on by a few tied up bits of wire

For anyone planning on doing this job on a petrol turbo car:
1. Unplug the ECU and the relay box next to it. Move the lot over to near the windscreen out the way
2. Remove the ECU housing (2x 8mm bolts)
3. Jack the car on the drivers side, support on an axle stand as well.
4. Remove the drivers side front wheel and the plastic wheelarch lining (lots of torx screws, most will have rusted to the point you need to use pliars/molegrips to shift 'em. They're all angled upwards so WD40 won't do anything
5. Remove the undertray from underneath the front of the car. 3x 10mm bolts at the front and 2 10mm washered nuts at the back, but beware the nuts are attached to some stupid little thing which a) will break and b) will be a pain in the rear to grab through the small hole with a pair of short-nosed pliars. Do the drivers side first as you'll be able to see what you're up against. You'll have to do the passenger side blind if you don't fancy taking the wheel+liners off that side as well (you won't!)
6. See the tensioner? WD40 it! See the square hole in it? Shove a 3/8in ratchet in it, put a 12in minimum extension bar on the end of the ratchet, and turn anti-clockwise. You may have to work it a bit first before it'll shift. When you've gone far enough, a 4mm allen key can be shoved in the little hole to lock it in place. Be extremely careful you don't knock the car off the stand/jack like I did! It does require a MASSIVE amount of torque to shift - I had 18in of leverage and needed more so I could free a hand to put the allen key in.
7. Cut the belt off. Don't waste time trying to work it out, you'll spend enough time trying to get the replacement in. Took 20 mins of fiddling before I had it
8. Do the above in reverse to get your car back in one piece. You may need to drill the undertray and use zip ties to hold it on

I really can't see why such insane torque is needed to shift the tensioner! I really don't want to work out the numbers for what it'd take to need 2 hands at 18" of leverage, but it's a hell of a lot!
I'm glad I managed it though!
Next weekend (if the weather's good and my back's recovered by then) I might have another crack at the cambelt. I figure the only sensible way to attack it is to remove the ECU box, the vacuum valve (I think that's what it is) and *shudder* the engine mount