Is it the first?, I got one a couple of yrs ago that what touted as the "first", I got some for £10 at the time. I remember because I got 5, one for each of my nephews and nieces.

Just looked at the site, you linked, it does say "one of the first", and I have a feeling that I got mine for a company called "Royal Mint", not the actual Royal Mint, I dunno. You might know the company, they send out offers by post alot

Ahh!, found it https://www.londonmintoffice.org/silver-coins/sovereigns , 2019 looks about right too, and I definitely paid £10 each