As @ainsworth74 noted above, it is due to a bad redirection in place. For those of a technical bent, it's a HTTP 302 redirect in place for https://www.railforums.co.ukStarted today and same happens in Edge and Chrome.
The same is not in place for https://railforums.co.uk$ curl https://www.railforums.co.uk --head
HTTP/2 302
cache-control: public, max-age=2592000
content-type: text/html; charset=UTF-8
date: Sat, 10 Sep 2022 15:46:08 UTC
display: staticcontent_sol, orig_site_sol
location: https://www.railforums.co.uk
pagespeed: off
response: 302
server: Apache
vary: Accept-Encoding,User-Agent,Origin
x-ezoic-cdn: Hit ds;mm;141ac3dbdef66e2f45ff07f0220f9251;2-248012-1;aa0f8561-0aa5-4e88-66b8-3f902c41c67c
x-middleton-display: staticcontent_sol, orig_site_sol
x-middleton-response: 302
x-origin-cache-control:
x-sol: orig
$ curl https://railforums.co.uk --head
HTTP/1.1 200 OK
Date: Sat, 10 Sep 2022 15:48:53 GMT
Server: Apache
X-Frame-Options: SAMEORIGIN
X-Content-Type-Options: nosniff
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: private, no-cache, max-age=0
Set-Cookie: xf_csrf=mRLPqTIfpeGPCpKA; path=/; secure
Last-Modified: Sat, 10 Sep 2022 15:48:53 GMT
Content-Length: 112583
Content-Type: text/html; charset=utf-8
TL;DR: Don't put the www in the address bar (or remove it from links) and you should be okay.