I think this may be a more common problem than people realise, try it out and let me know.
Issue is that my site ranks higher in google.com than in google.co.uk.
There seems to be no logical explanation for this...my domain is a .co.uk, my hosting comapany is UK, the host IP address is in UK. Why would it rank higher in google.com?
If you're going to try this out then you can't just put www.google.com in the address bar as it will automatically default to google.co.uk when you press ok. The way to test it is to perform your search on google and then when the results are displayed change the ....google.co.uk/search..... in the address bar to ....google.com/search..... and then press 'go' in the browser (do not press 'search' on google as it will default back to .co.uk again).
Sorry, just realised that most of you are probably in US anyway so your default will be google.com anyway...but there'll no doubt be some UK readers...