How do I open the engine fusebox on 2002 Mk6 Ford Fiesta?

I need to open the fusebox in the engine bay of my 2002 Mk6 Ford Fiesta 1.4 TDCi, (the one bolted to the side of the battery holder) as I think I have a problem with the fuse for the sidelights, tail lights and dashboard lights.

I can't figure out how to get the fusebox open to check the fuse, and as usual the Haynes book shows you where the fusebox is but not how to open it to check the fuses.

Can anyone help me please, while I still have some hair left after tearing it out trying to get it open!

Thanks.