We have nowhere to walk into. You have to provide the paperwork, send it off to a nameless person in a nameless office, and if they agree, you get a positive reply. If not, they'll send back the paperwork, with more questions to be answered.
I've generally had a good response from them when dealing with Rovers - simply because they're not worth a huge amount. I have had issues with classic Jags in the past, to the point where they threatened to deregister my E-type while I was in Afghanistan, and accused me of falsifying the chassis plate - simply because they'd mixed up the letters and numbers on the V5 (logbook).
It took pictures of the original chassis plate, and copies of Heritage Certificates along with Jaguar reference books showing how the chassis number was formed, as well as the threat of legal action against them, before they issued a new V5 - but never admitting they were at fault.