If you do a site: search using Google UK's 'UK results only', the index pages of ten .com domains and three .net domains (out of 65 that I manage) are not listed.
1) All sites hosted in the UK across 4 different servers in 3 different DCs 2) No link exchanges, very little outward linking, no excessive inward linking. No inter-linking. These are not directories, MFA, affiliate. They are contact/services offered websites for UK companies and sole traders. Some are dynamic, some static. Size from under ten to under one hundred pages. 3) No canonical issues, no dupe content issues, no over-optimisation. I use the same techniques and links for all my sites. Number of affected sites has not grown since this problem was spotted. Unaffected sites re-cached this week. 4) Internal pages all listed AND RANKING for their terms.
Would other UK based webmasters like to share their experiences? Perhaps we can collectively contact Google and refer them to this thread.