There is no set amount you are allowed to retain in your account to meet ongoing bills, but clearly if you are in an IVA and are building up a large cash balance then the calculation of your disposable income payment may be questioned.
The same answer applies if you are BR. You need to save your allowances, so providing you don't have thousands there won't be a problem. Also, I have never had to send the OR any bank details for my new (post BR) account.