London Registrars Ltd

Company Secretarial Practice for PLCs -  Many people think that all PLCs are listed and that their shares are traded on a stock exchange, but that is not the case: you can have a “private” PLC, provided that it adheres to the basic rule that the PLC must have at least two directors, a suitably qualified company secretary who is on record with Companies House, share capital of at least £50,000 (of which a minimum of 25% must have been paid into the company) and a trading certificate has been obtained before the PLC starts trading. In addition, a PLC’s accounts need to be audited by a statutory registered auditor.

http://www.london-registrars.co.uk/company-secretarial-services/basic-company-secretarial-services-for-non-listed-plcs-by-subscription/