It shouldn't be needed as the Insolvemncy Service will ( should) report the completion to the credit agencies. But, if you do it as well, you will have the comfort of knowing it has been done. Go on to the agency's website and search the 'Contact Us' details. Or, you cab drill down to your get a copy of report and use the 'report an error' button, which should prompt the agency to contact you.
It is an idea, while you have the 'certificate', such as it is, in your hands, to get several photocopies, and even, if you have the means scan a copy into your computer (makes it easier to send out if needed). Tuck the original paperwork away somewhere safe. Mine was issued 7 years ago and I have never needed it again --- but some do.
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