Update on the headlight.
MotoGB finally got back in touch with me today and the news isn't good. MV are unwilling to replace the headlight as the bike is 10 years old and has passed all its previous MOTs without an issue.
MotoGB are however willing to send me the offending part at cost price so that I can fit it myself. Awaiting a price on this because I have a spare headlight unit lined up and ready to be sent from a guy on the MV forum.