Leasehold Reform, Housing and Urban Development Act 1993

17 (1) Except where the demised premises consist of or include any unit let or intended for letting on a business lease, the lease shall not include any provision prohibiting or restricting the assignment of the lease or the sub-letting of the whole or part of the demised premises.

(2) Where the demised premises consist of or include any such unit as is mentioned in sub-paragraph (1), the lease shall contain a prohibition against—

(a) assigning or sub-letting the whole or part of any such unit, or

(b) altering the user of any such unit,

without the prior written consent of the lessor (such consent not to be unreasonably withheld).