Just in case anyone else is in the same boat - my primary ntlworld.com email is ok and was fixed shortly after the problems of 19/20th June. The problem I had was loss of my secondary ntlworld email and historic emails on that account.
To access my secondary email I simply log into my primary email and the secondary one is listed lower down the same page. However, the secondary email has been showing an exclamation mark in a black triangle, which when clicked on states 'The entered credential or authentication information does not work or are no longer accepted by provider. Please change them'.
It still shows this for my secondary email if I log into my primary email account so this evening I opened an 'incognito' window and tried to access my secondary email that way. It opened straight away, I could access it all and all my historic have been restored.
I don't understand why the secondary email is now locked on my primary email but at least I can now access it directly through either an incognito window or a different browser.
Maybe this will help someone in a similar position.