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The two changes are to Google's existing Quality Score and Ad Rank systems.

Every ad that goes through Google has its own quality score, which is calculated through a complex formula based on a number of factors -- the most important being how many times the ad gets clicked.

The higher the quality score, the better the chance that the ad will appear near to the top of the Google search results page, within the first few pages.

This traditionally meant that ads that had been clicked more times would appear closer to the top of the page, even though they were more likely to be clicked simply because of that position.

Google now measures the click-through rate of an ad while taking account of its position at the time it was clicked, which should increase overall quality scores.

The second change affects the way ads are shown in the yellow region above search results.

To appear above the search results, ads must meet a certain quality score and have the highest ad rank, or page position, because of the likelihood of being clicked.

In the past, if the ad with the highest ad rank did not have a high enough quality score, then no ad would appear above the search results.

Google has now changed the settings so that if an ad in position one does not have a high enough quality score but the ad in position two does, it is possible for ad number two to jump over ad number one and appear above the search results.

This means that more ads will appear on top of Google's search results.

In October, Google changed its stance on prohibiting gambling websites from advertising through its AdWords programme.

Google's third quarter results showed that profits had risen 25% from the same time last year to £780m.