It seems inline with the BBC charter (it's a non-service activity which supports learning for people of all ages [one of the BBC's stated purposes], and helps fulfil the requirement that the BBC must promote technological innovation), so it would seem to be a reasonable use of license fee income. It could be seen in a similar vein as the BBC Micro, which was designed and built by Acorn.

http://downloads.bbc.co.uk/bbctrust/assets/files/pdf/about/h...