Only the information that you give him or her. They can ask you for any 'reasonable' information to assess and monitor your finances and refusal can have consequences. They will also have any information the creditors share to validate their claims.
They are not 'linked' to HMRC, or any government body.
My opinions are merely that .. opinions based on experience. Always seek professional advice.
IVA Completed 23rd July 2013 .... C.C. 10th January 2014