At common law a company is limited to acting within the objects set out in its memorandum of association.
Anything purported to be done by a company which is beyond those objects would be 'ultra vires' and void at common law, and the directors could be personally liable for such acts.
From 1.10.2009, the common law rule is subject to CA 2006, sec31(1), which provides that, unless a company's articles specifically restrict the objects of a company, its objects are unrestricted.
Companies registered before that date will have an objects clause in their memorandum of association. Any provision in such a company's memorandum is now to be regarded as being in the articles (CA 2006, sec28). In practice, the problem of being bound by a statement of objects has has for many years been avoided by many companies specifying in the memorandum that the company is a 'general commercial company' which, by CA 1985, sec3A, could carry on any trade or business and had power to do all such things as are incidental or conducive thereto. From 1.10.2009, most newly formed companies are registered without objects, and older companies will, over time, adopt new articles with no restriction on the company's objects.