As I understand the system -
The Aircraft and flight ID's, and locations are decoded by the receiving box, the local box then translates this information into aircraft and route.
The receiving box, somewhere in South or South-West UK seems to have decoded the aircraft Mode-S incorrectly - NOT John,
The flight-ID is another matter, partly as to why it was showing near Portsmouth why even the hold should have been North of Heathrow.
The direction of the flight also looks incorrect for the SHT13 routes!!!