How to change washer on Beaumont Brassware tap?

[Tommy Peanuts]

After managing to unscrew the top cowling of this tap, I can see a nut underneath. But I can't budge it. I'm assuming I should be trying to unscrew it, or should I be doing something else to sort this out?

Photo here

Any advice gratefully received.

 

[Dan Robinson]

You need to undo the mechanism using the faces you have exposed. It will need a decent spanner, equal and opposite force on the spout and you to eat your weetabix.