Gabs, a moderator at Search Engine Roundtable Forums, discovered an interesting way of determining how to find supplemental results on .co.uk domains.
According to his blog post, if you click on "Search for Pages from the UK," you will see the Supplemental Results only. If you click on the "Search the Web" radio button, you will see all regular non-Supplemental results:
Ok so you have a .co.uk and your using the site command to check the number of indexed page but by mistake you have the “pages from the uk” selected.. Bammm.. Only sup’s are returned..
The problem is that google.co.uk is pretty much filtering out the UK results into the supplemental index.
I was able to reproduce this instance with one of the leading e-commerce sites in the UK. In the first screenshot, there are 7.1 million results that are not in the supplemental index:
But in this second result, where only pages in the UK are being searched, there are over 44 million results. Notice how all of them are tagged as a supplemental result.
This is indeed a nice find, but I don't think google.co.uk was meant to work this way. It would be neat if we can have a tool that does this more easily though, so for now, this will suffice for UK folks.
Forum discussion continues at Search Engine Roundtable Forums.
