Turns out it’s not only Windows 8 that has its telnet client disabled, Windows 10 is in the same boat. I’ve been using Windows 10 for quite a while now and just discovered this issue. Anyway, the way to enable is as follows:

• Right click on the start button
• Select “Programs and Features”
• “Turn Windows features On or Off”
• Select ‘Telnet client’ in the dialog box that appears, like here:

  

Job done.