Your overdraft should be included in your IVA and should not be used. Have you changed your bank account to a non creditor?
Sharing from experiences of dealing with debt
The greatness of a man is not in how much wealth he acquires, but in his integrity and his ability to affect those around him positively.
Bob Marley. http://kallis3.blogs.iva.co.uk
As Kallis says the overdraft will be a debt included in the IVA and any overdraft facility will be withdrawn. It would be wise to move bank accounts to a bank you do not owe any money to -- they should not do so, but they might try to take money from your account to cover the debt to them.
I am concerned that you have been told £100 per month for 6 years "and that's it" --- 'that' is rarely 'it': You have, I hope, had it explained that you will also have to pay over a portion of any overtime, bonus payments and pay rises, as well as any windfalls (lottery wins, inheritances and the like).
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014 http://foggy.blogs.iva.co.uk