This Q&A considers the effect of a share buyback on a company and its directors where it has subsequently been discovered that a shareholder did not own all the shares that they purported to sell to the company. It gives a brief overview of the legal position and does not consider a claim under the tort of deceit in relation to the shareholder who has potentially misrepresented their position regarding the ownership of the shares. This Q&A assumes that the purported share buyback is an off-market share buyback carried out by a private limited company. Part 18 of the Companies Act 2006 (CA 2006) governs the acquisition by a limited company of its own shares, ie a share buyback. CA 2006, s 658 states that a limited company must not acquire its own shares, whether by purchase, subscription or otherwise, except in accordance with the provisions of CA 2006, Pt