I found that Vodafone broadband was intercepting my DNS requests to Cloudflare. Using cloudflared[0] to enable DoH on my pi-hole resolved this.

[0] https://docs.pi-hole.net/guides/dns/cloudflared/

Thanks! Will look into that.

Even more insidious sometimes is that Virgin Media seem to silently block some VPN websites.

They may have given up by now but think of those children they saved!

Actually that Virgin is keeping on with this unethical practices. There are posts popping up almost weekly in various VPNs' forum and it always about their speed are so low (dial up/DSL speed) or they reached the timeout. And Virgin don't support IPv6 (it look like they are starting to support IPv6 but they plan to impose 20Mbps cap on IPv6 connection) and IPv6-in-IPv4 tunnel will 99% to fail to connect or stuck in the loop until timeout.

Double check that your DNS settings is correct. I'm on BT and it's working fine for me. I've previously used it on VM fine too.

Ah, talktalk may just be being lazy (or the sci-hub change hasn't hit me yet)