Why do I get two different result sets?

[bobo.cx]

Hi - not been doing this stuff for a while so I am a bit out of touch with latest developments with Google. Anyway, I have been doing some work on a site that wants to rank for 'fine furniture'. I am in the UK, the clients business is in the UK, and the clients site is hosted in the UK on a .co.uk domain.

When I search in Google for 'fine furniture', I have noticed that I get two different result sets.

One set of results shows me, as I would expect, mostly results from the UK and mostly results from .co.uk sites. This result set also identifies my location down the left hand side of the page and sometimes shows a map on the right with local search results.

The other set of results shows me, almost exclusively, .com sites which are mostly in the US. This result set does not show my location in the left hand column and never shows any local search results.

I have not been able to establish what triggers one result set or the other. I am at the same computer at the same location. Sometimes I am logged into Google and sometimes not, but there seems no correlation with being logged in and which result set I get.

Can anyone tell me what's going on here? I can post images of the different results if you like, but I have tried to make the above explanation clear.

The frequency of each seems about the same - i.e. each around 50% of the time. So is it some kind of round robin algorithm?

I can understand that some queries are global in nature (e.g. 'seo tips') and some are inherently local (e.g. 'emergency plumber') so perhaps with 'fine furniture' Google can't decide and so alternates between the two?

...but I am just theorising based on limited facts, so if someone actually knows why this is happening I would appreciate if they enlightened me.

Thanks!