Allocations are on a strict first-come, first-served basis to qualified applicants. There are no territorial restrictions: applicants need not have any connection to the UK.
.co.uk is by far the most used of the domains, followed by .org.uk. .plc.uk and .ltd.uk are only rarely used.
The intended restriction of .co.uk to companies are purely nominal; in practice it is open to any and all applicants. Likewise, whilst .org.uk is for organisations, there are no restrictions on registering domains. While .me.uk originally had no restrictions on registrants it has since been tightened up to require registrants to be natural persons (i.e. not companies, etc).
However, registrants in .ltd.uk must be, and remain, private limited companies incorporated under the UK Companies Act 1985. In addition, names can only be registered if they correspond (in accordance with the algorithm in the rules of registration) with the exact company name, as recorded at the companies registry at Companies House. The same conditions apply for .plc.uk, but for public limited companies. Neither of these domains are widely used.
.net.uk is more open, but the Nominet regulations still mean that a registrant must be an ISP, or a similar body, and that the domain is not used for providing services to end-users. .nic.uk, however, is limited solely to domains operated by Nominet.
.ac.uk domains are intended for the use of higher education institutions (beyond compulsory education age), and are also used by some academic support bodies such as the Universities and Colleges Admissions Service (
www.ucas.ac.uk), public research establishments, and learned societies such as the Royal Society (royalsoc.ac.uk) and the Royal Institution (ri.ac.uk). Primary and secondary education uses .sch.uk.
Unusually, .sch.uk domains are allocated at the fourth level, with the third level being taken up by the name of the local education authority (LEA) e.g. someschool.lea.sch.uk. For example, Tiffin School in Kingston upon Thames has the web address
www.tiffin.kingston.sch.uk. Previously applications were made in the normal way, but after Nominet came to an arrangement with the education authorities, one domain per school was issued automatically.