A more recent version of these Land Licences, Leases And Prop Estoppel notes – written by Oxford students – is available here.
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P R O P R I E TA RY E S T O P P E L Prop estoppel is a form of action alone - confirmed in Thorner v Major  Lords Walker, Neuberger and Hoffman all agree prop estoppel can impose a duty on A to B.
Supervision 9 LICENCES Thomas v Sorrell  a licence "makes an action lawful which, without it, would have been unlawful". A licence is a liberty which does not form part of a legal and equitable property right. 5 main varieties:
BARE LICENCES: Exists where B has a liberty to make use of A's land in some way - A is free to revoke that liberty. Can be implied e.g. door-to-door knocking, unless expressly revoked. A under no duty not to revoke the licence Wood v Leadbitter  held in Winter Garden Theatre v Millennium Productions  that A's revocation does not immediately turn B into a trespasser - has a reasonable time period to leave, which is the only mechanism the court needs to explain why revocation does not immediately become trespassing, explains Hill. Bare licence does not impose any duty on X, a stranger, not to interfere with B's use of land. If B has a licence and A transfers his freehold to C, there are 2 ways in which B has a right against C: (i) direct right, and (ii) pre-existing proprietary right. Direct rights e.g. contract with A to continue the licence, but why would this happen? Any preexisting proprietary rights would exist independently of the licence, confirmed in National Provincial Bank v Ainsworth  that a licence is definitely not a property right.
Requirements:statement/action by D, who ought to appreciate C relying on it, an act by C in the reasonable belief that he has or will have an interest in the land, induced by the statement/action, consequent detriment to C if D is entitled to resile from his statement/action.
1. An assurance by A --- must relate at least in part to the land, can extend to personal/property rights of A. It must have been understood as intended to be taken seriously by B - Crabb v Arun DC 
assurance consisted of words and actions in the form of the gap in the fence for B to pass through. Held in Thorner v Major that the assurance must be reasonably clear, not made in family/domestic context. Pre-contractual negotiations? Certainty will depend on context - can include later events; precontractual negotiations etc... Where the context is commercial, courts much less likely to find prop estoppel - Yeoman's Row v Cobbe .
2. Reliance by B --- B must show that he has relied on A's assurances. In domestic contexts, reliance is presumed, Greasley v Cooke  and Wayling v Jones  where even though B admitted he would have stayed with A had the claims not been made, he had still made sufficient sacrifices.
3. Detriment to B --- vital question is would B suffer detriment if he had no prop estoppel claim?
Sledmore v Dalby  detriment is judged not at time of assurance, but at later point. Held in Gillet v Holt  that even if B does benefit in some way from some aspect of the arrangement, as long as such benefits do not outweigh the prejudice B would suffer, the claim is allowed. The extent of A's duty to B Need to know extent of A's duty to B, generally held that if the parties are bargaining, the court will award full assurance, if there is no bargaining/agreement, proportionality comes into play. Held in Henry v Henry  that "proportionality is at the heart of the doctrine". B will receive full assurance unless it is disproportionate to do so, if it is, the court exercises a wide judgemental discretion. This makes for unprincipled results and Gardner suggests the problems of determining extent lie in the lack of clarity over the justification for this doctrine. Priority: Structure depends on asking whether B, at the time of the sale to C, had the property right in the land: is it legal or equitable?; does C have a defence?: B's position before the court order is made --- before court order, B only has estoppel equity, does this equity bind the purchaser?
Registered land - s.116(a) LRA 2002 - means B's interest will bind C if (i) he has protected it by a notice, (ii) is in actual occupation. McFarlane says there is a problem with this because where the right was not an interest in land in the firs time, it could become one by virtue of s.116? Goymour submits this view is incorrect. B's position after the court order is made --- at the time the court is made, B has an immediate equitable interest in A's land, unless the court chooses to recognise the right as a monetary right (becomes a personal right).
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