One man's opinion:
http://www.sportinggun.co.uk/shootin...sh_Prince.html
My opinion is that it's just what the English call a half-pistol grip.
Some smaller bore Parkers had half grips. I'm pretty sure I've seen several .410s stocked that way.
Checkered side panels on a V grade tells me it's either been restocked, or it's hiding a pin that was put in to repair a split head.