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I've just typed "Private Investigator" into Google, location set to "Coleshill" (it's near Birmingham!)
The search results were surprising:
Position 6: <cite class="_Rm">birmingham-privateinvestigators.co.uk</cite>
Position 8: <cite class="_Rm">privateinvestigator-coventry.co.uk</cite> Both sites are the same source of information altered to suit the city - INCREDIBLY SPAMMY. They are just full of SEO text stuffing. No doubt any city you enter they will appear with [city]-privateinvestigators.co.uk..
How are they ranking with such old-skool dirty SEO tactics? You can't say they will be found eventually, because Google has released algorithm after algorithm updates to penalise sites like this.

Could it be the importance of having a local phone number and (supposedly) physical address?

Hi, what does it mean when a lot of our keyword phrases rank only when "UK" is typed in the search term?

For example:
"boxes" (not in top 50)
"boxes UK" (38)

"big storage boxes" (45)
"big storage boxes UK" (33)

We haven't attempted to SEO the pages for search terms with "UK" appended to them. Our domain is a co.uk domain. So, what reasons could there be that are we ranking in such a way?