Thanks for your very understanding reply, nice to chat to another Webley pistol collector on here. I have two Seniors around the same numbers and with the common D stamp. I have also got an older slant grip with the serial number of 246 and stamped H under trigger guard, not mentioned in Hillers guide. So I was hoping for something to bridge the gap.
As for your amazon link to Gordon Bruce's Webley Air Pistols: Their History and Development.... Nice one........
Cheers
Carl