Thanks for taking a look wheel and for reporting your findings.
The Robots.txt is a blank file. What would you suggest I place in the file in order to permit all crawling from all search engines?
Now, strangely enough I compared the date of my previous change of host: also from the US back to the UK .. the dates largely match.
The site was indeed excluded before - back in 2008. The issues then were obvious and easy to fix - primarily related to linking and a lack of attention to detail.
Having learned my lesson then, I literally didn't make a single major change to the site for 3 years precisely because I was terrified of it being dropped again.
Zoom forward three years and the site is six years old. It's been bobbing between page one and page three for all that time and any changes have been tiny.
This time I decided to rewrite some URLs and condense and present my content better on some pages. I discussed this with a member here at WebmasterWorld and he was very gracious in offering his expert advice.
Now, it could well be that the site doesn't deserve to be ranked where it had been prior to last week. BUT - and this is the crux of the matter - there is no way it deserves to be excluded from the first 1,000 results.
Wheel: if you do a keyword search for my main keyword, which I'm sure you can guess, you'll agree that if anything my site is of a far higher quality than half of page one.
Moreover, whilst it -could- be a coincidence that the site homepage was dropped as soon as I switched hosts from the US to the UK, I'd say that's a pretty big coincidence.
The site is fully indexed as it has always been, but the homepage is simply excluded for all and any keyword searches.
I read an article recently which sums up the problem:
With Google filters the website usually remains indexed with similar Page Rank, but SERP filtering is applied which all but removes the site for all or specific keywords.