Section 51 | Reasonable price to be paid for a service
From legislation.gov.uk
(1)This section applies to a contract to supply a service if—
(a)the consumer has not paid a price or other consideration for the service,
(b)the contract does not expressly fix a price or other consideration, and does not say how it is to be fixed, and
(c)anything that is to be treated under as included in the contract does not fix a price or other consideration either.
(2)In that case the contract is to be treated as including a term that the consumer must pay a reasonable price for the service, and no more.
(3)What is a reasonable price is a question of fact.