I have had a knocking sound for a few months now and have just jacked up the front of my RR to find about 10mm of movement in the ball joint on the driver side front lower arm, so I know this needs to be replaced and I probably shouldn't drive the vehicle given the state of the ball joint.

I also had slight movement in the passenger side suspension which looked like it was the inner track rod joint. Could this have been false 'reading' give the state of the driver side lower arm ball joint, or is it likely that I have wear in the track rod as well.

Just after some opinions before I put an order in to Dan in the morning (unless my local stealer has one and I can get it fixed tomorrow) 56 TDV8 Vogue SE
9 Freelanders, 2x 2002 TD4ES, 2001 TD4, 2002 1.8GS, 2000 XEDI, 2x 2000 1.8ES, 2004 1.8 & 2000 1.8 GS (rolled)
91 Lotus Carlton (sold)
90 Lotus Elan (BRG)

I had the same thing. I was concerned the inner track rod was away as it seemed to me there was more play than I would have expected when I inspected it.. But when the lower suspension arms were changed, as you are about to do, that completely cured my fault and although the inner track rod was still the same there was no noticeable steering movement when driving.
I take it you are replacing both arms at the same time?  Previously..
Vogue SE TD6
Defender 90 2.4
Defender 110 TD5
Vogue 3.5 EFI

Was hoping to get away with just doing the one, but probably false economy, typical RR repair project creep. I will do both arms  56 TDV8 Vogue SE
9 Freelanders, 2x 2002 TD4ES, 2001 TD4, 2002 1.8GS, 2000 XEDI, 2x 2000 1.8ES, 2004 1.8 & 2000 1.8 GS (rolled)
91 Lotus Carlton (sold)
90 Lotus Elan (BRG)

That is both arms done, it seemed so easy to start with but both ball joints were a nightmare.

Broke my screw type ball joint separator and had to get a fork type separator and batter it with a 20lb sledge hammer to get the joints to separate.Took 1/2 an our to do one side and over an hour to pop the ball joint on the other side.

Also sheared off the 10mm fixing for the height sensor on the drive side. Hopefully I can get one from the local stealers, held on with a 10mm bolt at the moment. All the other bolts came apart easily.

How have others who have done their front lower arms managed to tighten them with the vehicle back on the ground, I had to use about 4 extension bars as my breaker bar was too long to turn under the vehicle 56 TDV8 Vogue SE
9 Freelanders, 2x 2002 TD4ES, 2001 TD4, 2002 1.8GS, 2000 XEDI, 2x 2000 1.8ES, 2004 1.8 & 2000 1.8 GS (rolled)
91 Lotus Carlton (sold)
90 Lotus Elan (BRG)

With the car at normal height, you should slacken off the big bolt that goes through the rubber bush. This makes sure the rubber is not twisted/stressed, then tighten it up as much as you can. I thought mine was tight but it would give a crack as it moved when turning at low speeds. 47p2 put it up on his ramp and tightened them properly for me. Previously..
Vogue SE TD6
Defender 90 2.4
Defender 110 TD5
Vogue 3.5 EFI