The adoption of .uk has been a little slower than most would have hoped. Whilst I'm in no doubt that .uk will eventually become dominant, there are certain things that Nominet could do to hurry it along.
It would be a great help to Nominet if they were to publish anonymised data that said that some big companies were losing xxxxx number of visitors a day because they weren't using their .uk.
Most people in countries outside of the UK expect UK businesses to be on .uk - from their point of view why would we be on .co.uk?
For example my bet is that there is a fair old number of people outside the UK typing Tesco.uk into their browsers in the hope of finding their site. OK, they have the .com but the point is that some won't.
If Nominet can some how get hold of data that says a particular UK company is losing xxxxx visitors a day by not using .uk, but doesn't name them. This will have a massive effect on hundreds of companies who would fear that they (because Nominet haven't given any names) are the ones losing traffic. They would then go and register the .uk, either forwarding it to their .co.uk or placing their site on the .uk
The change for .uk will come from thee top down, it would be so much easier to get 10 big companies to change to .uk than it would to convince 100,000 small sites to change. However if those 100,000 smaller sites watched as Tesco, Asda, etc all moved to .uk - they would follow.
Though I'm not 100% sure if it would be Nominet that has this data or it would be a Telecom's provider that would need to provide it.