A company which is controlled by another company (its holding company (www.practicallaw.com/A36248)). Whether or not one company is a subsidiary of another depends effectively on whether the other company:
Holds a majority of the voting rights; or
Is a member and has the right to appoint or remove a majority of the directors (www.practicallaw.com/A34876); or
Is a member and controls, alone, under an agreement with other members, a majority of the voting rights (section 1159, Companies Act 2006).