4.—(1) In the case of any transfer to which this Schedule applies, a joint certificate by or on behalf of Network Rail and the undertaker that—
(a)any property specified in the certificate, or
(b)any such interest in or right over any such property as may be so specified, or
(c)any right or liability so specified,
is property, or (as the case may be) an interest, right or liability which was intended to be, and was vested by virtue of the transfer scheme in such one of them as may be so specified (and, if it is the undertaker who is so specified, that the property, interest, right or liability has not been transferred back to Network Rail by virtue of an agreement under paragraph 9) is conclusive evidence for all purposes of that fact.
(2) If on the expiration of one month after a request from either Network Rail or the undertaker for the preparation of such a joint certificate as respects any property, interest, right or liability they have failed to agree on the terms of the certificate, they must refer the matter to the Welsh Ministers and issue the certificate in such terms as the Welsh Ministers may direct.