I have a lovely condition pre-war straight grip Senior in .22, and an equally as lovely pre-war straight grip Mk.I in .177. I also now have two extra sets of bespoke made replica walnut grips for my Mk.I, too, which have been made to the exact same original spec and design as the originals.
Being something of a horder, these extra grips are for if (when) any other Mk.I's come my way, which may benefit from a good set of grips to set them off (so many sets of said grips have been lost and/or damaged over the years).
One of these sets of bespoke original pattern walnut Mk.I grips hosts an original Webley brass flying pellet button, and the second set, a reproduction brass coloured plastic (but you'd never know it was plastic) flying pellet button, and all are very lovely -- very lovely indeed (and all are mine, mine, mine).