Losing a precious instrument to a low-life is an ever present problem for any gigging musician. What sounds worse about this is the probability that the person who stole it knew exactly what they were taking.
I routinely photograph instruments and record the serial numbers, but knowing this won't be much comfort to Damien. I can only suggest what's already been suggested; visit local swop-shops, keep a good eye on EBAY (you can put search requests on EBAY, and they'll tell you when a similar item turns up for sale)and get round a few music shops with details of the banjo.
Is that Newcastle in the North East, or Newcastle down by us in the Potteries?
Good luck.