"A person who is admitted to a hospital in pursuance [to such] an admission order ... shall be treated for the purposes of the 1983 Act -- (a) as if he had been so admitted in pursuance of a hospital order within the meaning of that Act made on the date of the admission order; and (b) if the court so directs, as if an order restricting his discharge had been made under section 41 of that Act, either without limitation of time or during such period as may be specified in the direction."