I find that odd as there was a lady on the radio earlier explaining how she had confirmed her status by showing only one document which was a statement from HM Revenue & Customs confirming the years of payments of national insurance contributions, something which i did myself a few months ago with great ease.
Then if this criteria is acceptable to the Home Office, they have the power to access NIC Records. All they need do is request an NI Number and check the records themselves without the need to even contact anyone, let alone ask them to fill out forms and provide documentation