I ve just removed the ball joint bolted the new one in place but cannot locate the upper fixing bolt into its socket , do I need to compress the spring before I can do so ?

I assume you're talking about the ball joint on the lower front wishbone, I've just done these on my sons car, a FL1 but the same set-up so far as I can tell.

I used a spring compressor to get the taper bolt in but I also had to lever the wishbone down with a long bar, disconnecting one end of the ARB drop link made it a bit easier though.

Thanks Clive, got both sides done , job was much easier with a second pair of hands.

Glad you got it sorted

I found the hardest bit was to drill out the rivets

Yeah , one of the drive shafts also came out, fun times. But both sides now done.