Thank you for your response. On my pc I use Outlook as my email client but everything works fine there. On my Android Samsung A6 phone I use the Google email client, Gmail, and with it the hyperlinks are inactive for my ntlworld account but are OK for my other two accounts, Gmail and Outlook.
Prompted by your suggestion I have tried using the Samsung email app and hyperlinks work fine for all three accounts there. However I am now well used to using the Gmail app and would like to continue doing so - any suggestions how to correct this issue?