Hi Jon,
You have my sympathy. When I bought my 3 litre X-type 2nd hand from Jaguar a few years back, I was amused to find the V5 and the DVLA records all showed that chassis and reg no. as being a 4.0 litre S-Type.
I was less amused when it meant I couldn't get it road taxed or insured until Jaguar at Brown's lane sorted out the mess with the DVLA... Fortunately it only took 10 days. It could have been worse I suppose.
You know what they say about computers, garbage in, garbage out. Sounds like someone at the DVLA screwed up your re-registration.
I can't agree with your comment about the poor performance of the Silver Spirit. Have you any idea how much power it takes to accelerate a stately home to 60mph???

I think Rolls-Royce always suggested their power output was 'sufficient'. No clues there then
I'm sure if you drove it nicely you could get the mpg into double figures (just!)
Cheers,
Glenn.
Glenn.
1989 XJR-S 6.0.
2001 X-Type 3.0 Sport.
Both in British Racing Green.