Fakes of these have been around for ages and can be had on EBay for very little money, two piece bi-metal badges with a slider on the reverse.
The Kipling and King "Bible" however shows that the badge was in fact one piece in brass (or "gilding metal").
Couldn't believe my luck in picking up this one, the first good one piece brass piece I've seen in over 40 years.
According to a source in the Corps who had researched this badge it was introduced in 1904 during the reign of Edward VII but never officially authorised and was worn only in very little numbers, in fact just by one single detachment of the MFP in Shorncliffe, the unit in fact which had proposed the design of the badge in the first place.
A truly rare badge.