I became curious as to its origin so set about trying to ID it.
As the badge was found in a marine location my first contact was the Navy Museum and as they did not recognize it they referred me to the NZ National Army museum who had no trouble sorting it out as follows:
Thanks for the photo; this is a New Zealand Regiment Hat Badge - Second Pattern. The NZ Regiment was formed in 1947 when the troops returned home from WW2, the old regional regiments (Such as the Wellington or Auckland etc) were disbanded (Later to be turned into the Territorial forces) and the troops all became part of one Regiment.
24/2/11 Update: More historical information from the National Army Museum.
The badge is in reasonable condition for having been about 200mm underground although the silver and gilt plating is long gone.