On the wheel end, if the drive is too close to the fork to get a set of grips to the knurled ally, slacken the wheel spindle a couple of turns. That'll allow the speedo drive to rotate (the axle acts as a big pinch bolt). Once you've rotated it slightly, you should be able to grip it OK.
Morning Jools,please do keep me informed...think i need to get to get two pairs of long-nose pliers,as the knurled bit goes into a threaded part,which in turn goes into the drive and the two are turning together,when i think that the threaded part should stay still in the drive...
Mine was easy in the end, bit of rag wrapped around the knurly bit to protect it, pair of pipe grips, quick twist, job done.
The threaded bit isn't supposed to turn as well though, that is a problem Moggers.
My speedo drive is OK, but the speedo cable is snapped. Only had the tiniest stub of cable sticking out above the threaded portion, just enough to drag it out.