"If the established rule is to the effect, as it is, that a person seeking rights of residence here on grounds of marriage (not being someone who already enjoys a leave, albeit limited, to remain in the UK) must obtain an entry clearance and then seeks to remain on marriage grounds, having no other legitimate claim to enter, would in the absence of exceptional circumstances to justify the waiver, disrupt and undermine firm immigration control because it would be manifestly unfair to other would-be entrants who are content to take their place in the entry clearance queue in their country of origin."