Names like .gov.uk currently have special status. If something ends .gov.uk then I know it has that special status that separates it from .co.uk. The implication is that it's vetted.

Allowing non-special commercial entities to claim their own .uk names will undermine this. government.co.uk is currently squatted but is obviously a commercial entity and not the Government. What will happen when government.uk gets squatted? What about all the other combinations?

Allowing direct .uk registrations will increase confusion and reduce security.