Formal validity of a will — s.9 execution

An 80-year-old testator in England signs his written will, intending to give effect to it, while his neighbour and the neighbour's adult daughter are physically present together and watch him sign. The neighbour signs as a witness in the testator's presence. The daughter leaves the room to answer her telephone. Ten minutes later she returns and signs as a witness in the testator's presence, after the neighbour has gone home. Neither witness benefits under the will. Capacity, knowledge and approval, and freedom from coercion are undisputed. Is the will validly executed?