It just started an hour ago but it seems whenever there's a webpage with one of those high fangled moving ads, it causes the whole screen to flicker, even when I minimise the offending page, other internet pages seem to flicker as well, only way to stop it is to shutdown the webpage completely or go somewhere else.

Does this sound like something I should panic about or will it pass?

It might be overheating for some reason. If it's an older card, sometimes the fans get very dusty and can come to a complete halt, burning the card.

If you can have a look at your card (physically), it would be reassuring, perhaps. It could also be a problem unrelated to your graphics card, but it's worth having a look anyway.

I have no idea what a card looks like let alone where to look, annoyingly this machine is conviniently over a month old so it misses the 30day warrenty   :(, it was a factory made machine bought online so I don't have any cover (not that I could afford it anyway :D)

If it's that recent, then it won't help to have a look, it probably still looks new.

I was thinking, maybe it has something to do with your drivers. Do you experience any kind of flickering while gaming? You could always try to download the latest drivers off your video card manufacturer's web site (ATI/Nvidia).

Clean your fans they're a lot of dust in it probably.

I second updating drivers, could you tells us what model graphics card you have?