Hello Mark
My partner and I delved quite deeply into this topic, assisted by a thread here on the JOC Forum entitled "Recommended Independent Garages".
We have a '07 S and a '07 XK; Fixed price servicing was available at Jaguar main Dealer but, frankly, we found some issues difficult to pin down and found it annoying having to get past the "pretty people" in front of house. Consequently, we delved into Independent Jaguar Garages and were pleasantly surprised, at least with our choices here in the Midlands.
Our view is that if you locate a Jaguar Specialist, you are going to have folk working on your Jaguar who are familiar with the model/s and, consequently, not be spending large amounts of time head scratching and making do. We have found that our "Indies" are cheaper (sometimes considerably so) than main dealer, and can give a thorough rundown on what needs doing, what has been done etc. In other words, they are specialists.
We would not entertain taking either of our Jaguars to a "generic" outfit, such as you have mentioned (manufacturer service schedule) and most certainly wouldn't sit comfortably with the other option which you mention. £107 for a full service wouldn't, in our view, be far off the cost of the parts let alone the labour. And what is the source of the parts, whose been flying around the countryside in your car etc etc. We are quite sure that such generic places have their place, but for a 6 year old Jag.....maybe not! (Just as an example, one generic outfit that we know off told an ex-colleague that the timing belt change on his diesel S-type was an engine out job, purely because that is the procedure with the LR Discovery that uses the same engine; in fact, although the timing belt change isn't a job for the faint-hearted, it ISN'T an engine out job!).
All this, of course, is just our opinion but we do bring to mind the old adage "don't spoil the ship for a ha'porth of tar'.
Whatever, happy growling and we hope you reach a conclusion with which you sit comfortably