Google UK Market Share: 83%

The exact figure doesn't matter. But can Google be accused of monopoly pricing?

I don't think it can because the amount you pay for a click in the AdWords system is largely dependent on what your competitors are prepared to pay.

If they bid aggressively then you have to. But Google doesn't (usually) set bid prices. The market does.

A business that doesn't set its prices can hardly be accused of exploiting its dominant position.

I actually think there was an issue recently with this when Google introduced very high minimum bid prices for some keywords for some advertisers. Keywords that cost 5p a click would suddenly be made inactive unless you bid £5 a click. This was all part of the "Google slap" as it was known.

At that point I think it could have been argued that it was exploiting its dominant market position. But those high minimum bid prices have gone away as of September 2008.