In some countries, as far as I'm aware, if you are able to hire service on a website, it's illegal not to be able to cancel it through the same channel (i.e. without having to call, email, go to a branch, or any other option).
Is this legal or illegal in the UK?
If I recall correctly, when I subscribed to Sky Broadband, I did everything online. However, now that I wanted to cancel the service, I had to get in touch with them.