Martin Pipe enlisted the help of Michael Dickinson, the now US- based trainer who saddled the first five home in the 1983 Cheltenham Gold Cup, in the preparation of Granville Again who hit form on the day it mattered to scoop the £ 140,000 Smurfit Champion Hurdle.   Following the same victory route as his full brother Morley Street two years ago, Granville Again fought off the challenge from 50--1 shot Royal Derbi to win by a length.   Halkopous, who had been in line with the first two turning for home, faded to finish third, with King Credo fourth.     Extra special Numerically, Pipe has re-written  the racing annuals, topping the double century mark in the last four consecutive seasons.     But this win was extra special -- his first in a top championship event.   With a little gentle persuasion, Pipe encouraged Peter Scudamore to switch from his intended mount Valfinet, who finished 16th, to the winner who had fallen two flights out when poised to strike in last year's race.   With a smile, the champion jockey recalled "For a long time I was always going to choose Valfinet because he has done so well and Granville Again was running terribly.