They're trying to serve a different audience in each of those addresses. Obviously the content should be different for a search conducted in Birmingham, Chicago, or Kolkata.

You should try to see that your site targets the correct country and language on HTML level. You can also change the desired country from Google Webmaster Tools. TLDs co.in and co.uk are geotargeted to respective countries which might help. Then there's the content, but there's a lot of good articles out there.

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Google.co.in is for India.
Google.com is for US.
Google.co.uk is for UK.

So it is obvious to show different results. Make your Site with High Quality Unique Content. And Quality SEO(High Quality PR Do-follow links), SMO by Targeting US and UK to get the better results in Google.co.uk as well as Google.com

Because they are some different locations. They're trying to give you the best results based on the location.

Thank you for your replies. Most appreciated.

Results are always localized in Google based on the users Geographical location.

Google.com is for worldwide whereas other extensions like .co.in and .co.uk are for specific countries.

If you want to promote your website for particular country then go for that relevant extension domain name.

Hi,

Google.com, Google.co.in, Google.co.uk will show respectively USA, India & UK search results. So we will see some differences in keyword rankings.

Regards,
Reddy Sekhar Reddy.K
SEO Analyst.