UPDATE 12th Feb 2019.
My Car is now fixed.
The mechanic recommended to me by Old Peter (Carl - based in Erdington, Birmingham) took my car away last night and brought it back just after Midday today having replaced both EGR valves. My Jaguar S Type 2.7 Twin Turbo now drives like new again.
Whilst there was only one EGR fault code indicating just one faulty EGR valve, it seemed a false economy to replace just one.
Carl charged me £420 and also replaced a blown tail light bulb for me. The EGR valves are Lucas OE parts (not budget parts from China) and there is a 12 months parts and labour warranty.
An excellent job and super speedy too.
I have to send out a big 'thank you' to Moderator/Staff member Old Peter for his continued support and assistance with this problem.
My one fear when buying this car over 9 years ago was the potential costs for parts and repairs but thanks to Old Peter and this forum I am a very happy Jag owner once again.
I also thank the other members for their contributions.
Regards
Keith