“Having regard to the context in which it appears, I doubt very much whether sub-paragraph (iv) was intended to do more than make it clear that, if A had a right of drainage or some similar right over the land of B itself which was not itself void for perpetuity, ancillary rights of constructing and repairing works to make the basic right effective were not to be treated as void for perpetuity because they might be exercised outside the perpetuity period. To construe sub-paragraph (iv) as validating grants of rights of drainage or similar rights to arise at some uncertain date in the future would lead to very odd results.”