www.jec.org.uk

Been reading this is quite common with the XJS and I'm getting it with mine. Guessing I need to pull the spare wheel out and check the various leads from the tank to check for leakage?

Yep!
Also check the over axle pipes where they exit the boot; I had a perished hose there.
A common spot is directly under the tank where it rubs on a rivet head but that requires the full tank removal to sort.
I would disconnect the battery before prodding about in there.

as Steve said, could be one ( or more ) of many known issues

this is how I did mine the other year

viewtopic.php?f=46&t=9444&hilit=fuel+tank

BB

That sort of job is going to beyond my ken (and toolbox), BB, but I will check the various leads, etc., after disconnecting the battery. If not, I'll add it to the list when I visit The Jag Workshop.

Strange, my fuel odour has diminished after the car has not been used much, and did not return after a long run at the weekend. But what did return was the fuel pump whine. I wonder if perhaps the two are related?

fuel pumps can make noise for two reasons,

one , the pump is FUBAR and needs replacing

second, the pump is experiencing restricted flow, either pulling from the sump tank , or pushing to the engine end , change the external filter, and remove and clean the under battery sump tank , the pickup tube has a fine mesh filter which clogs

BB

Lots of discussion in Kirby Palm's on-line XJ-S book for those who have not yet discovered it:

http://www.jag-lovers.org/xj-s/book/Jaguar.html

Hi Mac - it's worth checking the breather lines and making sure they're OK. There is a hose that comes from the filler overflow and then goes down through the lower quarter behind the wheel. If that is dislodged you will get some fumes. I knowing this because that happened a while ago. It got much better after I fixed that.
I've never had the tank out to check for corrosion as I've never really felt it was that bad. I always kept a gallon can of petrol in the boot and blamed any slight whiff on that!
Before you condemn the tank, I have never changed the pipes. They are probably original and possibly have become porous as they've hardened. I think the 5% methanol inclusion in modern fuels doesn't help older rubber compounds that were never built to cope with it. So maybe it would make sense to change those for ones better suited to modern fuel recipes before going to the hassle of taking the tank out?
The swirl tank was taken out and cleaned a couple of years ago - I think there's a thread on here somewhere from when I did it and a picture of the crud I got out!

fuel pumps can make noise for two reasons,

one , the pump is FUBAR and needs replacing

second, the pump is experiencing restricted flow, either pulling from the sump tank , or pushing to the engine end , change the external filter, and remove and clean the under battery sump tank , the pickup tube has a fine mesh filter which clogs

BB

I recall reading a procedure for draining the sump tank involving something like bridging terminals on the fuel pump relay, does anyone have details?

this is usually a short cut to ' pumping the tank dry '

easy really

take off the fuel pipe from the pump to the fuel supply tube, place this pipe ( or an extension attached ) into a receptacle for the fuel ,

the fuel pump relay will have x4 terminals identify the load or secondary terminals, and placing a suitable wire between the two spades will provide power to the pump without the car running,

warning

the pump can get hot if overworked in one go ,

BB