Does he still have the head? If so then can you recover it?

You could also send a statutory demand (http://www.insolvency.gov.uk/pdfs/forms/6-1.pdf) which is the precursor to a bankruptcy petition. In this case it would be a bluff because a) bankruptcy only applies if debt > £1000 (assuming it's not) and b) it costs £150 to file a petition, in addition to any legal costs. But he probably wouldn't know that and it might scare him into paying you back by any means possible!

HTH
Chris
aka the master of getting paid by crap promoters