Quick Google - no idea of the veracity.

Members' power to require directors to call general meetings (sec303 - sec304)
The directors must call a general meeting if so requested by the holders of 10% of the voting shares (or 10% of the voting rights if no shares). If at least 12 months have elapsed since the last general meeting called under this section, the request may be made by 5%.
The request for the meeting must state the general nature of the business to be dealt with and may include the text of a resolution to be moved at the meeting (provided the resolution would not be ineffective (e.g. under the Act or because contrary to the company's articles, etc., and provided it is not defamatory, frivolous or vexatious).
If the request is properly made, the directors must within 21 days call the meeting for a date not more than 28 days after the date of the notice calling the meeting. If the request included a proposed resolution, that must be included in the notice, which will then be part of the business that can be conducted at the meeting. (If it is a special resolution, the notice of the meeting must say so, in accordance with sec283, above.)

Source: http://www.companylawclub.co.uk/topics/calling_general_meetings.shtml