Employment status: Tour guides engaged on "casual as required basis" were not employees

In Carmichael and another v National Power plc 18.11.99 House of Lords, the House of Lords holds that two women who accepted a company's written offer of employment as tour guides "on a casual as required basis", and then worked as guides on invitation when they were available and chose to work, were not employees under contracts of employment. The issue of whether they were or were not employees did not turn exclusively on the construction of the documents; and even if it had, there was no obligation on the company to provide casual work or on the women to do it.