What if a notice to quit is served by one joint tenant of a lease but was induced by a misrepresentation?

In Potter v Dyer ([2011] EWCA Civ 1417, CA (Eng)) P’s parents granted him an oral tenancy of a farm. He assigned it to himself and C. C left the country. Some years later, D, the new owner of the farm, served notices on P under the Agricultural Holdings Act 1986 requiring him to carry out repair works at the farm. P disclosed the assignment to C and himself as joint tenants. C served notice to terminate the joint tenancy (thinking that this would leave the tenancy on foot but release her from any future obligations under it). P argued that C had been induced by D’s misrepresentation. P argued that as a result, the notice did not terminate the lease but operated simply as a surrender of C’s interest under the joint tenancy. This failed. If there had been a misrepresentation C would have to elect to affirm the notice or to rescind it. There was no support in the authorities or in principle for P’s proposed ‘middle way’.