A document required to be served personally on a prisoner must be served on—
(a) if the public trustee is manager of the prisoner’s estate under the Public Trustee Act 1978 , part 7 and the proceeding is of a property nature or for the recovery of a debt or damage—the public trustee; or
(b) if paragraph (a) does not apply and the prisoner has a litigation guardian—the prisoner’s litigation guardian; or
(c) otherwise—the person in charge of the prison in which the prisoner is imprisoned.