I finally went for it and ordered a Philips SPC900 webcam from Amazon, which is actually being sold through Pixmania, but the postage is less through Amazon than purchasing it direct with Pixmania – strange.
The Philips SPC900 is costing me £46 delivered. Now after trying my Logitech Pro4000 webcam I can actually compare both the webcams when it comes to astronomy use, and luckily the webcam adaptor that I purchased for the Logitech Pro4000 webcam will still fit on the Philips SPC900.
I also noticed on my travels that you cannot buy the Logitech Quickcam Pro4000 anymore as it has been superseded by the Logitech Quickcam Pro5000, but I imagine after looking at the logitech website that the CCD chip and insides are the same as the 4000, the best price though if you are looking at the 5000 does seem to be PCWorld at around £30.
As soon as I get it and get a clear night, I shall try it out and report back with comparative images from both webcams.