Vodafone.co.uk allows the purchase of a pay as you go eSIM from its website. Right now they have a deal where you get unlimited UK and Ireland calls and 27 GB of data for £10 per month for 3 months (and I cancelled the auto-renew feature.)

In the sign up process, they ask for a street address that they will use to validate the credit card - and it accepts UK addresses only. I had the thought that perhaps Cap1 doesn't care about my address because all foreign online charges with Cap1 get referred to the Cap1 site for validation.

So I used the address of my my hotel, and the Cap1 card. A popup window popped up from Cap1, I validated (I don't remember exactly what it wanted), and the charge went through.)

I wonder online sign ups will increase over time? If so, could be trouble for the eSIM vendors, who can't come near the 27 GB for £10 I got from Vodafone.

The UK also has no KYC rules, which makes the signup process easier.