Here is my updated time line. We applied together with my wife as "married couple living at the same address".
Application=NCS (Southwark)
Date of submission or posting 17/02/2006
CRITERIA - 5 yr stay (4 + 1 yr ILR)
Date of debit of cheque = 21/02/2006
Date of receipt of acknowledgement = 25/02/2006
Date of approval = 06/04/2006
Date of receipt of approval = Sometime between 13/04 to 22/04. As we were on holiday, I don't know the exact date. It was at the bottom of the pile of mails so I'm guessing that it was nearer to 13/04
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The approval letter said that we should contact Weybridge Citizenship Service as we live in Surrey. The earliest date for a group ceremony was 31 May in Kingston, so I asked for a private ceremony in Guildford and they were able to arrange it for next Wednesday (03/05) for £75 total for both of us.