"holding company", if that other company:
* holds a majority of the voting rights in it, or
* is a member of it and has the right to appoint or remove a majority of its board of directors, or
* is a member of it and controls alone, pursuant to an agreement with other members, a majority of the voting rights in it, or if it is a subsidiary of a company that is itself a subsidiary of that other company.

The second definition is broader. According to s.1162 of the Companies Act 2006, an undertaking is a parent undertaking