Good quality sections on ebay at great prices.

 

Yes, several of us have had full custom systems from MIJ Performance in Birmingham, other places do a similar thing, around £500 for stainless on an X/S type or X350 with a lifetime guarantee, but you might get cheaper for your car.
Here's a previous discussion http://www.jaguarforum.co.uk/f27/guess-whos-going-mij-tuesday-25629.html

 

Hi driverjools, I am in the process of doing this on my x300 now. I have bought an aj6 engineering cat back system. I have already fitted the fully stainless back boxes, these were roughly £350 and they are the finest you can buy. I have since ordered cat replacement pipes and replacement pipes for the silencers under the rear seat area. This will link the back boxes to the down pipe and primary cats and was £400. Not the cheapest system but I should have gained an extra 10-15bhp and I'll also see torque and mpg improvements. Loads of choice out there, depending on what you want from your new system.

 

Thanx for all your replys.....some very helpful advice......think I'll get a stainless custom system, I've just found a place quite near me so I'm going to see what they can do Stainless Steel Exhaust Manufacturers | Sports Exhaust | Classic Exhaust and Manifolds.....