O’Reilly v. Mackman [1982]

Dictum by Lord Diplock in
which he acknowledged importance of Anisminic,
which ‘liberated English public law’ from fetters that courts had
previously imposed upon themselves, ‘by drawing esoteric distinctions between
errors of law committed by such tribunals that went to their jurisdiction, and
errors of law committed by them within their jurisdiction’.
Anisminic breakthrough came by recognising that where
tribunal whose jurisdiction was limited by legislation mistook law applicable
to facts as it found them, it must have asked itself the wrong question ie one
into which it was not empowered to inquire.
Its purported determination
was not a determination within meaning of empowering legislation and was
accordingly a nullity.