Cheers Griff.
I ended up making a tool out of a long bit of copper pipe bent into a long thin 'Z' shape which hooked behind the remains of the seal allowing me to knock it out with a mallet.
Job done :)
New front hubs in, diff oil changed and an oil change and last night I drove from Kent to...
Deep apologies if this is covered anywhere else (I've looked and couldn't find my particular problem).
I'm changing the passenger side front hub/bearing assy on my 1999 TD5 and I thought I'd change the leaking oil seal on the drive shaft while I was at it.
No problem getting it all to bits but...