IIRC DB Regio/Arriva had been reported to be storing some of their mk.3 carraiges at Bletchley TMD... from what i can remember it was mostly the mk3s purchased after the demise of Cargo-D, that were expected to be stored at the site once they were released from/by Barrow Hill.
but im happy to be corrected if im wrong...
Showing on TOPS at Bletchley TMD (location 70302) are...
11046, 11019, 11030, 11054, 10237 and 11044.
Maybe someone can shed some light on those numbers?