This is a conversion kit to convert a Farish OBA to an OEA covered van. This wagon was built by British Rail as a one off but it ran on flows in England, Scotland and Wales, so it can add a bit of interest to your Speedlink rake wherever you're modelling.
You can read about the real wagon on Paul Bartlett's briliant site here.
You can my posts on how to prepare the OBA for conversion in my RMWeb thread here.