Thanks all, that makes sense on the BD-5J.

I think Little Nellie is G-AVDH, the real ARZB is at Old Warden and is covered in stickers and the reg is in a different place. I have checked my photos from Reymerston Hall and the one at the Film Museum matches up with the same one there. From a big of digging around it turns out that while painted as ARZB it is actually AVDH.

Cheers

Rich