9.27 'do so'

'Do so' is used to mean 'perform the action just mentioned'. The various forms of the verb 'do' can be used. This structure is rather formal.

• A signal which should have turned to red failed to do so.
• Most of those who signed the letter did so because of her involvement.
• She asked him to wait while she considered. He did so.
• British governments are perfectly capable of improving drinking water quality, and perhaps they should voluntarily have done so before now.