.uk is a cleaner simpler version of the UK domain extensions that are currently available. In a technical sense there is no reasons for the .co in .co.uk, it simply serves no purpose. From a branding point of view .co is worthless and dilutes your brand.
Those that chose the option of .co.uk for their sites didn't do so because they wanted the .co ( it means nothing), they did so because it was the most important domain platform in the UK at that time. Times are changing and the .uk will be the primary domain platform in our opinion as many brands continue to move to it.
To be absolutely clear the .co.uk will not end, it will just become the second tier of the UK Internet as brands move to the top level which is the .uk. Those that want to continue using the .co.uk can do so and their sites will continue to work indefinitely.
Other domain name extensions such as the .com and .de (Germany) are already on the second level as are many other countries. Other countries are also moving to open up their second levels - Japan co.jp to .jp , New Zealand .co.nz to .nz and Australia are now considering the same move from .com.au to .au
Why are they moving now?
Around 2012 one of the larger registrars provided a survey that showed a desire by their customers for the option to move their sites up from .co.uk to .uk
This was then passed up to the organisation which administrates all domain names that end in .uk, they decided to consult its members on whether or not they should allow direct registrations under .uk
There were two main questions :-
1) Should organisations and people be able to register directly under .uk?
2) Who has the first rights to register the .uk domain name when they become available?
The answer to the first question was a positive yes, as most respondents would be happy to see .uk domain names become available. Respondents cited everything from that it looks better from a branding point of view, typing is easier on mobile devices and it is easier to remember for worldwide customers outside the UK. There were numerous other reasons but the overwhelming majority were positive to change to the new better .uk, the release mechanism allowing registration of the new names had to be right.
The second question regarding who has first rights to purchase the .uk was the main issue. If Nominet didn't get this right, most said that they did not want to go ahead with .uk
With so many third level extensions (.co.uk .me.uk .org.uk etc) competing to register the .uk equivalent of their names, Nominet were never going to please everyone and In our opinion they got it right by giving first priority for a limited period of time to the current .co.uk holders.