Yes, I received a response from the BM. It took 8 days and seems to have been sent around a bit. I've ended up with a response from the National Finds Adviser for Iron Age and Roman Coins.
Their opinion is that it is a die trial piece! Excellent news. Just what I was after. But, it gets better - they think its a Paduan trial piece. I dont have one of those so thats pretty darn cool! I wasnt expecting roman so this is much better than the alternative (a lead fake from the 90s).
The FLO hasnt got back to me but it should be being photographed around now.
If anyone has the book Imitations and Inventions of Roman Coins could you please take a photograph of pages 50-51 - thats the reference I was given y the BM but I dont have a copy!