Simon
I have recently with others completed a book trilogy on the station histories of the Met which we started in 1998. Our latest 'Discovering more behind the blue lamp - Policing Central, North and South West London' had an introductory chapter on MP helmets (as did our 2nd), plates and helmet furniture through the ranks. I have attached a very early page from Gaunts pattern book which may be helpful and is illustrated in our book
Also a helmet plate from 1870 - 1876. There are those who think this badge was only issued to Dockyards but this is wrong as I have at least 6 CDVs which I can date to various divisions during this time. The star pattern did not come in until around 1876. I attach a copy of the image
I have also added an Inspectors and Chief Inspectors helmet plate
Peter
pcdogberry