So I have the jag running fairly well now so its onto matters.

The brakes seem pretty good with a bit of a hard pedal when driving.
After 20 miles or so the pedal begins to go to the floor and needs to be pump. If the car is given a cool down the brakes comeback.

Will a fluid change solve this issue or is there something else causing the issue?

Sounds to me like one of the brakes is hanging up. As it heats up from the constant dragging it boils the brake fluid. Once it cools down it goes back to normal.

Check all the wheels to see if they spin freely bt jacking up the car and turning them by hand. It shouldn't take too much force to spin them.

If the fluid has not been changed in the last few years, a change will be sensible, anyway.

If the car is NON-ABS, and the sticking-on brake pad is not found, it might be that the master cylinder is going home. It can happen that as the engine bay heats up, the seals in the MC start to soften, and do not work as well as they should. Again, if the MC has not been changed, it is a very good idea to do it.

Greg

The brakes don't feel like they are hanging up. The fluid is warm though, but so is everything in that engine bay!

As suggested above, check to see if one of the calipers is hanging up. This is one of the first steps of troubleshooting a brake problem like yours. Try jacking each wheel off the ground and turning it by hand. If you find one that doesn't turn by hand, you found the problem. If you take it to a shop, this is probably the first thing the technician is going to do. (On a regular car, the tech would feel each wheel after driving, and try to identify a hot wheel. However, the Jaguar has inboard brakes, so this won't work for the rear wheels.)

Brake fluid? When it doubt, flush it out! Repeat every 2-3 years.

I've had only one experience with boiling brake fluid. It's not something I'd want to go thru ever again :-)

Cheers
DD

Right I will check each wheel. I think you mean the rear wheels are the ones you can't check by feel due to the inboard brakes.

Ahh yes, you're correct, I meant the rear wheels!