Wilburforce - 11:30 am on Sep 7, 2006 (gmt 0)

My (UK hosted) .com index page dropped out of Google's UK index (still high position globally) on 14 August. All other pages on the site were unaffected, and there had been no recent changes to that page.

The index page was back to normal on 17 August (again no changes at this end), and stayed that way until this morning, when the same problem reappeared (yet again, no changes at this end). Again, only the index page is affected, and it is only affected (at the time of this post) on:

66.102.9.99
66.102.9.104
66.102.9.107
66.102.9.147.

In the meantime, I have noticed the same thing has affected a competitor's site (also a UK supplier of a UK-only service, also .com), but the effect certainly isn't universal. We're both in the top 5 for main relevant search term internationally.

The effect - as far as I am concerned, anyway - is limited to UK-only searches on google.co.uk.

It looks to me as if Google is trying out some kind of filter (although why it should only affect the index page defeats me, unless it is a trial with intentionally limited scope).

Any more ideas out there?