I feel, that Nominet are just after the money, so giving away freebies may not suit them.
However, it will cause chaos, and make some people some money. If you got the .uk free, to a .co.uk you own, (I presume) there would be nothing to stop you flipping it right away? Even if it cost just a fiver, its not a massive amount.
So, you could get domain.uk to go with domain.co.uk, flog .co.uk one week, and the next .uk, either to the same person or someone else, and you end up (again) with all the confusion that is the reason why lots of people really don't want this. While Nominet fatcats sit on the manicured lawns sipping Pimms at Henley and probably claim it all as expenses.