CA 18 January 1991. In October 1973 the plaintiff company (C) granted a lease on premises to F. In 1981 C granted an underlease to F on the adjoining property. Both lease and underlease contained identical covenants which included one forbidding assignment of the lease without the landlords permission. The new assignment would be registered with the landlord and a small fee paid. In 1987 F assigned their leases to a company H via a license , the defendants (E) acted as sureties . A clause of that deed held that assignment should be completed by 1 May and registered. Assignment was completed on 1 April but was never registered. H fell into financial difficulties and in June 1988 went into receivership . Writs were issued against the sureties E for non-payment of rent and breach of covenant . It was held at HC that the failure to register the transfer of the lease gave E a defence in that it made the deed null and void and that E ceased to have any liability on 1 May. CA however held t