What are is mirror principle and the main authorities?

For this question, I assume you mean within (UK) land law and the topic of registration. The Mirror Principle is the idea that the land registry reflects all the facts concerning the land and the title attached to it. The register must be an accurate reflection of the state of the land at any given time so that it may be relied upon. The main flaw to this (also known as the ‘crack in the mirror’) is the existence of overriding interests. The main authorities are found within: • LRA 2002 Schedule 3 para 2 (overriding interests) • LRA 2002 ss 23, 26, 29 (owner’s powers, protection of buyers/disponees, effect of registered dispositions) • Abbey National Building Society v Cann (what actions give rise to actual occupation and therefore a basis of an overriding interest) • Williams & Glyn’s Bank v Boland (overreaching trumps overriding interests; overreaching is where a purchaser pays the price to two trustees. Means any vulnerability faced by purchasers is solved when they pay money to two or more trustees)