DD:
Thanks for the details on that site, brilliant! I'll get into it a bit more tomorrow. Looks like London Sterling alright. The crowned leopard makes it pre-1822, and that style of letter 'C' puts it at 1818. Assuming 'I-H' are the silver-smith's initials, the artisan is most likely James Hyde of London, whose mark was registered in 1777.

The owner will be very interested to hear this I'm sure! Thanks again, DD, and thanks all for your appreciative comments.