Blued of DigitalPoint forum, says that base from his experience in the UK, if you have a site which ends .org.uk vs a site which ends .co.uk with the same number of backlinks with the same anchor text, then the .co.uk will appear above it for that associated search term.
http://forums.digitalpoint.com/showthread.php?t=1670199
SERP Monopolies are likely to become very common within the next 3-5 years.
