why is this? how much would that cost to fix?

Sorry, you're not providing enough information about your problem.

At any rate, the only way to really know how much it will cost to fix is to send the camera in to Canon UK factory service and let them figure up an estimate for you.

Also, keep in mind that ALL lenses will vignette a bit, especially when wide open and full wide angle. A stop or more of exposure at the corners is not uncommon. If you add filters or accessory lens adapters, it can get much worse. You really need to show an example for use to offer more of an opinion on the problem.

Visit: http://www.vanwalree.com/optics/vignetting.html and
http://www.the-digital-picture.com/Canon-Lenses/Canon-Lens-Vignetting.aspx
for more on vignetting.

thanks for replies, yes it looks exactly like the first link, fig 1 the left wall image but I've adjusted everything and lighting etc, it stays.

Is that to say the camcorder stays, or that you feel you have a problem that requires repair.

think it needs reapair or maybe the lens. it happens more when zooming in close.