Theft Act 1968

6 "With the intention of permanently depriving the other of it"

(1) A person appropriating property belonging to another without meaning the other permanently to lose the thing itself is nevertheless to be regarded as having the intention of permanently depriving the other of it if his intention is to treat the thing as his own to dispose of regardless of the other's rights ; and a borrowing or lending of it may amount to so treating it if, but only if, the borrowing or lending is for a period and in circumstances making it equivalent to an outright taking or disposal.

(2) Without prejudice to the generality of subsection (1) above, where a person, having possession or control (lawfully or not) of property belonging to another, parts with the property under a condition as to its return which he may not be able to perform, this (if done for purposes of his own and without the other's authority) amounts to treating the property as his own to dispose of regardless of the other's rights.