Somebody like Vintage ATCO would know better than I but I THINK, from memory, when we extended the "parallel taxiway" to Alpha 1 in 1999 that made it an average of 26 movements / hour. Obviously it depends how much runway length each movement takes and whether they have to taxi to the dumbells and do a 180.
With departures on 24 having to enter at charlie and backtrack, it would have been significantly lower before that. With full length taxiways it would match Gatwick - perhaps as high as 50-60.
Really needs a better technical experts opinion, that is my guess.