Dear TJ,
I have silently followed ur posts and all the comments even the one by adebola in the blog for Nigerians on this subject matter.Now, listen to this.I applied for UK visa in 2008 and submitted bank statement from FBN.My statement was confirmed from the bank!It is not true that there is no signed document permitting them to check ur account balance.Ur mere signing the application form after it has been clearly spelt out that backgroud checks may be performed, is a form of aythorization.Infact, it is thesame right that can make them check ur employment record that can also make them chk ur account.
My final word, please walk into ur bank tomorrow and ask if the embassies usually verify account statements.Make sure u go to a standard branch,preferably the biggest in ur environment wish must have got a lot of experiences on immigration matters.Any information u get there should be taken as gold standard.U may post here for all of us to learn from.
I am not saying it is a crime to withdraw from ur account, only that u have to be careful not to go below the required fund for ur family size as u don't know how and when verification will be made.
All the best my brother.