CA 19 December 1988. Appeal by underlessees (L) from previous decision in favour of underlessors (M) concerning the construction of clause in a rent review . A formula contained in the review clause in the underlease referred to the rent in the headlease; it contained no reference to a fair market rent. The dispute arose because the original headlease had been surrendered and a new headlease granted; this lease was expressly stated to be subject to, and with the benefit of, the underlease. The relevant clause in the original headlease indicated that the object was to reach a fair market rack rent of the premises. At issue was whether M was still entitled to a rent review in accordance with the clause in the underlease as they submitted, or whether the review clause ceased to be operative as L contended. CA followed Sudbrook Trading Estate Ltd v Eggleton (1983), where it was held that the rent review clause in the underlease was not void for uncertainty; the judge ordered an inquiry a