TrollBeGone

This extension allows you to filter comments beneath articles on the Guardian newspaper website by identifying those users whose comments you don't want to see. After installing the extension, an extra option ("Block Commenter") will appear on your context menu when you right-click on a commenter's ID. You'll then no longer see any comments from that user in future. Any replies to their comments will also be hidden. You can manage the list of blocked users via an icon that appears in the address bar when on the Guardian newspaper website.

Note, that this extension is no way affiliated with the Guardian and at any point the Guardian could make changes to their website that may cause the extension to stop working.