touch_me_hard: Maybe you should talk to her. She may be of help

Siena: I would say your transmission (Auto) is slipping. This will account for the engine rpm and road speed not matching - so engine speed rises, but the road speed does not match, as in it seems slow for the engine rpm. If you look at your rev counter versus your speedo, you'll notice a massive discrepancy. At 70 mph, your rev counter should display approximately 2,800 - 3,200 rpm. I would imagine now it's indicating about 4,000 rpm or even higher.

Transmission slip would indicate an internal fault, or low fluid. It could even be a bust torque converter. Check your fluid level, though your car having no dipstick, this is a job for a QUALIFIED engineer or dealership, not a roadside mechanic. Your Jaguar is fitted with a ZF5HP24 transmission, and it's pretty complex. The drain, flush refill and filter replacement is also not straight forward. I have a feeling your clutch bands are burnt. Has your trans had a fluid flush and filter replacement? Because dirty fluid and a clogged filter will also produce the symptoms you've described.

As per your fuel consumption no need really looking further. A slipping transmission is like driving in first gear continously, which will equate to high engine rpm. This of course will burn more gas.

A couple of questions - is your Check Engine light on? And your transmission display on your dash (P-R-N-D). Is it showing what gear you select, or is the whole display lit up / blinking?

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Euroclydon: the check engine light is on,never had a fluids flush or filter replacement. So which do i start with Sir?

Siena:

Start with an engine AND drivetrain scan. I'm willing to bet your engine check light is on, due to an implausible signal / communication error between your ECU and TCU.

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Euroclydon: I just contacted an auto mechanic and he said he does not have a scanner that is compatible wit Jaguar S-type engine,he said he would get me someone so am still waiting on him till monday.