The quick and dirty fix is to take the fan hub off - Draper do a wrench big enough for the bolt.
Then drill a couple of holes right through the middle and whack a couple of big bolts through it.
Baically, there is a disc that spins inside the housing that should lock up when you've put the bolts in.
Watch out of the oil though, heat the hub up and let it all drain out, or else it'll get spun all over the enigne bay and cause you a minor panic then you find it.
HTH
Orlando