No dedication or grant of a way shall be presumed or allowed to be asserted or established as against--
(a) the Crown, or
(b) persons holding lands in trust for any public purposes,by reason only of user, and this whether in proceedings instituted by or on behalf of the Crown or not, and whether such user commenced before or after the eighteenth day of October, one thousand eight hundred and sixty-one (being the day of the commencement of the Crown Lands Alienation Act of 1861 ).