OK, mystery solved. For anyone interested, this is a support for the rear seat in the 2+2. When I bought the car the rear had been pulled out by the PO and all the bits stored in a box. There was also a different seat base from another vehicle included and this support came as part of that. Somehow it got mixed up with my dash stuff in the storage process.
Apologies for any confusion. Freddo still safely ensconced in the fridge.
Cheers
Paul