Solle v Butcher, 
After substantial alterations to a building, the Landlord and tenant wrongly thought that house was outside the Rent Act and fixed its rent beyond its limit whereas it was within. Tenant, sued for overpaid rent. Landlord, claimed rescission on ground of common mistake and innocent misrepresentation.
Though the parties made a mistake as to the identity of the flat, nevertheless the lease was not void at common law. But the court granted equitable relief by setting aside the contract and putting the parties on the terms that the plaintiff should choose either to rescind the contract or pay the full agreed rent