I have worked for the same firm for many years. I was in a iva during that time and completed it successfully.
Now many years later the firm are carrying out credit checks amongst other security checks by a third party. If that third party ask the question have you ever had a IVA and I answer truthfully can my employer terminate my employment. By the way I never at the time received any I formation from the employer to say we had to notify them.
I am afraid that the answer to your worry lies in your employment terms and conditions. There have been several instances, in the past, where forum members have been credit / security checked by employers and none have, as far as I recall, reported any problems following the exercise.
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