It'll be interesting to see how this will roll out to the average registrant. It's a strange move from a non profit organisation who already have to deal with a surplus of money coming their way.
I'd expect £1xxx for NN and anything from £2xxx to £4xxx for LL (depending on the letters). Though there was a recent LL sale of around £7000 if I remember correctly. Sales would have to include both the .co.uk and the .uk to maximise the price.
Have a look at domainlore.uk for most recent...
I wouldn't put much faith in Sedo suggested prices for UK domains. LLLL co.uk's don't hold much value unless they mean something or it's an actual word. Even LLL.co.uk's could sell for less than £499. The most recent LLLL sale on Domainlore.uk saw LCDs.co.uk sell for a mere £60.
Interesting that the domain is owned personally by one of their team and not the company.
Anyway, he neglected to pick up the .uk - so it's sitting prettily in my GD account