Re: Fork it!
You don't seem to understand how the DNS works. There can only be one registry for a top-level domain. Nominet is the .uk registry. People simply can't take their business elsewhere if they want .uk domain names.
In principle some other organisation could be appointed to run .uk. But the mechanism for doing that is unclear. Who decides? How? And once that new organisation was appointed, you're back where you started because something needs to be put in place about governance, oversight, policy making, membership arrangements, contracts, etc, etc.