co.uk is the commercial second-level space of the United Kingdom's country extension, operated by the registry Nominet. It behaves like .com in daily use, with three differences worth knowing before you register: the registry's own rules govern it rather than ICANN's generic-extension contracts, the shorter plain .UK form of every name exists alongside it, and transfers between registrars use Nominet's IPS-tag system rather than the auth-code dance generic extensions use.
Who can register, and what the record looks like
co.uk registration is open: individuals and organizations anywhere may register, though consumer-facing UK businesses remain its natural constituency. The record, viewable through Nominet's WHOIS, carries the registrant, the registrar tag and the expiry. UK-resident individuals can opt their address out of public display. As everywhere, the registrant field is ownership: a co.uk registered by your web agency in its own name is the agency's asset until the record says otherwise.
co.uk against plain .UK, and the defensive question
Every co.uk has a sibling one level up: example.co.uk and example.uk are separate registrations. The rights-priority period that once reserved the short form for co.uk holders has ended, so the two can be held by different parties. The pragmatic play for a trading business is to register both, point the one you use less at the one you use, and stop there; the wider family (org.uk for non-profits, me.uk for individuals, ltd.uk and plc.uk for registered companies) rarely justifies defensive spend.
Transfers, expiry and the IPS tag
Moving a co.uk between registrars is a push, not a pull: you ask the current registrar to change the name's IPS tag to the receiving registrar's tag, and the name appears at the new company, usually without fees on the name itself. That makes co.uk transfers fast when the losing registrar cooperates and a support-ticket exercise when it does not, so registrar choice matters slightly more here than for generic extensions. Expiry follows a grace-then-suspension ladder ending in cancellation, and auto-renew remains the sane default.
Questions people ask about co.uk
Do I need a UK company to register a co.uk?
No. Registration is open worldwide; some other .UK family spaces, like ltd.uk, do require the matching UK registration.
Should I buy the .UK if I have the co.uk?
If the brand matters, yes: they are independent names since the reservation period ended, and the pair is cheap insurance.
Why did my transfer ask for an IPS tag, not a code?
Nominet's system identifies registrars by tags. Changing the tag on the name is the transfer; there is no EPP auth code in the .UK registry.