IEIM120120 - Exchange of Information: Inward requests: What can I tell the customer about the request?

The Competent Authority will provide advice about what you can disclose to the customer on a case by case basis; however, the general rule is that HMRC can disclose the minimum amount of information necessary in order to obtain the information.

The letter from the overseas Competent Authority must never be shown to the UK entity.  

It will not normally be necessary to say which jurisdiction has made the request or identify the particular international agreement under which the request has been made. You can show the UK entity a document if they are a party to the document in any case.  For example you could show a loan agreement entered into by a bank if it is that bank receiving the request. 

You must never disclose any details about the enquiries underway in the requesting state.