Many US broadband providers unhelpfully block access to some IMAP and POP3 services that are not their own. Usually, the simplest method of accessing email (and other “blocked” services) is to use a “trustworthy” commercial VPN service that will allow you to tunnel past the block. You may wish to consider a subscription service.
When speaking of commercial VPN services, it is necessary to emphasise the use of a trustworthy service - as, for brevity, some VPN services have poor reputation.
Whilst you a free to conduct your own research - and make your own choice - I suggest that you consider hide.me VPN. This service offers excellent speed, a reliable connection - at sensible cost. While you would generally be advised to avoid “free” VPN services, hide.me do offer a trustworthy free subscription tier. The free tier is “capped”, but will likely be more than adequate for your stated requirement of accessing your UK-based email.
If you do consider paid subscription tier, you would be well advised to sign-up from the hide.me webpage in preference to the in-App purchase - the former being cheaper and allowing up to 10 simultaneous VPN connections:
https://hide.me
hide.me VPN App (Apple App Store)
https://apps.apple.com/gb/app/hide-me-vpn/id953040671