My drivers seat height adjustment has stopped working.
It's as high as it will go, I can hear the motor click and try to move in both directions but its jammed.
I have the seat out but can't see how to try t solve this
Anybody have any experience with this problem?

 

So I found a few posts about this problem but no solutions
This morning I took the motor off, took the gearbox off the seat frame and found that the screw gear from the gearbox to the seat lever was jammed at its extreme position.
Grabbed the screw drive in a pair of pliers, using a couple of layers of cardboard to prevent damage to the gear and worked it back and forth and eventually it freed itself.
Worked it in and out a few times, lubricated with silicone grease and reassembled;

This shows the gearbox off the seat frame which allowed me to grip the shaft and work it loose again

So this shows it all back together again
Hopefully when the seat goes back I'll have height adjustment of the rear of the squab back again.

 

Just wanted to thank the original poster, just gave this a try on my wife's 04 VDP, she tends to put the seat all the way up where it seems to jam the worm gear and won't go back down. Applied grease to the worm gear and them rocked the dismounted motor back and forth by hand until it feed up, will report back on how it holds up (first thing is to reprogram the seat preset so its not all the way up).

 

Finally got around to investigating why the back of the seat squab would not go up and down.
Symptoms were that I could hear the motor running when moving the switch, but no movement of the seat. All other directions were working.
Freed seat from floor, rolled it on its side, removed the three T40 holding the gearbox to the seat rail, then two T20 that held the motor to the gearbox. Found a chewed up square drive cable.
Went to scrapyard and removed one from a passenger side seat (Jag catalog says the whole motor/gearbox is handed and so different part numbers for left and right seat, but I figured, correctly for once, that the drive cable would be the same - and more chance of passenger seat being in better, less used condition).
Installed that, and freed off and lubricated the threaded drive rod (probably the original source of the jam that caused the drive shaft to get chewed up) and all seems well, now I have loads of headroom and my knee does not hit the key.

Hopefully the photo below is self explanatory.

So if the motor runs, then this is likely the issue. If there is single clunk when you move the switch in either direction, it is probably the threaded rod that is seized, and if there is nothing, start checking fuses, wires, connector, motor internals etc.

Good luck.

Broken and okay versions of the drive shaft.