Thanks very much for all the help so far!

I've been outside having a closer look at this. I sat in the van before starting the engine and pumped the clutch pedal several times; there was no creaking of the pedal and the pedal movement was smooth. I drove a short distance (to move the van into the back lane for more investigation) and clutch pedal was still ok, so I'm thinking that this is something that starts once the engine has been running for a while, I'll do a test run this afternoon to test this theory.
However I've also noticed this morning that what I previously thought was a water leak from the windscreen onto the cab carpet between brake and clutch pedals isn't water at all because it's greasy and has an odour. I checked the brake fluid level and it needs topping up again and I only did it a few weeks ago. I'm not sure where it's leaking from though, I looked upwards from the carpet (see photos), but I can't see any sign of leaks from servo, master cylinder, or reservoir.
[IMG:512:384]
http://i198.photobucket.com/albums/aa78 ... s/002R.jpg[/img]
[IMG:512:384]
http://i198.photobucket.com/albums/aa78 ... 004R-1.jpg[/img]
I'd be grateful if someone could tell me what I'm looking at behind the steering column and boot, because this is looking like where the fluid might be leaking from. Everything above here (as far as I can see) looks to be dry.
The creaking clutch pedal symptoms that I described earlier, could they be linked to this fluid leak?
Tony