I have not heard of either of them closing IVA'ers accounts, so far.
We don't have a Co-Op bank near us, but this hasn't. so far, been a problem. I do 90% of banking online and can pay in funds, if I get cheques, cash, etc., at my local Post Office. You can open the Cashminder on the phone in a few minutes.
During the early days, setting up and settling in to an IVA will put you through every emotion you have, but, it's a relatively short period of turmoil, then you will be on your way to sorting everything out.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014