Safari won't let me sign in to BBC account

I want to sign in to my BBC account, but when I click on Sign in, the first error page says 'Safari can't open the page, the operation could not be completed, 'KCFErrorDomainCFNetworkError 303'.

When I reload this page the error message changes to 'Safari can't open Safari-resource:/Errorpage html because MacOS doesn't recognise internet address starting with safari-resource'.

I have been in touch with BBC and they suggested clearing history, cache and ensuring cookies are correct, all of which I have done. I have just reinstalled High Sierra and the updates, to resolve my issue, but this has not worked. After all this I still cannot access my BBC account sign in, but I can from my Windows tablet and phone. So where is the conflict with Safari? This has only been a problem since installing High Sierra... I think.