The shareholders of a company are listed in the Annual Returns (form 363) [so long as the share capital has been paid up] and is public information.
The annual returns contains the following information:
* the name of the company;
* its registered number;
* the type of company it is, for example, private or public;
* the registered office address of the company;
* the address where certain company registers are kept if not at the registered office;
* the principal business activities of the company (see Principal Business Activities);
* the name and address of the company secretary;
* the name, usual residential address, date of birth, nationality and business occupation of all the company's directors;
* the date to which the annual return is made-up (the made-up date).
And if the company has share capital, the annual return must also contain:
* the nominal value of total issued share capital;
* the names and addresses of shareholders and the number and type of shares they hold or transfer from other shareholders.
http://www.companieshouse.gov.uk//about/gbhtml /gba2.shtml