The United Kingdom has enjoyed a system of company registration since 1844. Today, company registration matters are dealt with in law, by the Companies Act 1985 and the updating legislation contained in the Companies Act 1989.
All limited companies in the UK are registered at Companies House, an Executive Agency of the Department of Trade and Industry. There are more than 2 million limited companies registered in Great Britain.
A Limited Company is a legal being/entity in it's own right. If a company claims to be a limited company , but are not registered as such, the principles or the owners of the company take all liability. You sometimes see contracts, leases or other legal documents signed by a person t/a (trading as) something limited. I take this to mean that you can call a company limited without it necessarily being registered as such.