Supreme Court Rules 2000

In any proceeding in which 7 or more persons –

are subject to the same or a common obligation; or have the same or a common interest in or in respect of, or are under the like obligations in respect of, a fund or other property; or otherwise have a common interest in any matter –

one or more of those persons may be sued or made respondent or may be authorised by the Court or a judge to defend the proceeding with respect to the obligation or interest on behalf, or for the benefit, of all persons subject to the obligation or having the interest.