sorry for your loss but nobody would know anyway as each vehicle has its own security.
You can only go to the garage that may be serviced his vehicle or to a Citroen dealership and they will need identification like the V5C (log book) and may be a utility bill. It all is down to security and protection against vehicle theft. They are not all harsh and money orientated and may do it for free or reduce charge.
bob
June 2013