Are you talking about the boot over the ball joint or the bushings themselves? The Ball joint is integral to the unit so the control arm needs to be replaced in it's entirety if it's bad. If the rubber itself is the only issue, you can by replacement rubbers.
The symptom of a bad upper control arm is a thumping or clunking over bumps. To test them you need a pry bar and there are a myriad of views on how to do that. You should see less than 1/8" of movement up and down using a pry bar. Now you want to be careful not to tear into the rubber boot but if it's already set...
I'm in the US but here is a UK supplier:
https://www.balljointboots.co.uk/index.html
You only need calipers to get you fit right and that's fairly easy.
If you need to replace the bar, Note, when Ford took ownership of Jaguar, they used the same control arms as on their Lincoln's, Thunderbirds, S-Type, X350's and XK. They are easily replaced and can be found for less.
Here's an example:
FRONT
MotorCraft MCSOE38 = Jaguar 6W4Z3084AA
MotorCraft MCSOE39 = Jaguar 6W4Z3085AA
Here's a link on eBay. These will fit your car
https://www.ebay.co.uk/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=6W4Z3084AA&_sacat=0