As far as I'm aware there are actually two builds of the Nexus in the UK - ERE27 for those who imported from the USA, and EPF21B for those who bought from Vodafone. Seeing as it's an ERE27 build that's been available first, I would assume (please tell me if I'm wrong) that those who imported from the USA will get updates before other builds.
The update should just come as a notification, but you can manually check under Settings -> About Phone -> System updates