And of course anyone can start a petition about anything. Just because they choose to place certain "facts" in the description doesn't mean it has any basis of truth behind it:
http://www.fbhvc.co.uk/news/index.htm
An HPI check will tell you of any plate changes on the car, but it doesn't necessarily follow that DVLA will re-issue a previous registration mark if you remove the allocation of a "cherished" mark from the car. The previous mark may be non-transferable, or may itself have been transferred, or placed on retention.