In Expression Web 4.0, if you need to change the options for spelling to cover UK spellings, you will need to make the change in two places:
Tools > Page Editor Options > General tab – Spelling:- Set Spelling language from the drop-down
and
Tools > Spelling Options > Custom Dictionaries > Set this to English (UK) as well from the drop-down.
The custom dictionary option to use UK English, or in my case NZ English – the only option for english is US English. This problem is affecting many other on the EW Forum