Have you been playing in the mud and water? That's a great way to trash the starter motor or solenoid. Sounds like starter motor or solenoid, could just be a wiring problem. Trouble is when a 200Tdi Disco engine is put in a Defender the starter motor disappears under the exhaust manifold. So depending on how well the engine has been installed you may be able to get to the starter and solenoid fairly easily and clean it all up or you may be looking at removing the exhaust manifold and turbo before you can even see the starter motor.
Good luck!
