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HMRC internal manual

Compliance Handbook

How to do a compliance check: establishing the facts: asking for information: asking informally for third party information, using GDPR/DPA exemptions

You can ask third parties to provide information about taxpayers informally.  The third parties may have obligations not to disclose the information, under data protection legislation.

However, legislation does contain some exemptions which allows third parties to disclose to HMRC. 

In certain circumstances you may be able to give the third party assurances that the exemptions apply.

(This content has been withheld because of exemptions in the Freedom of Information Act 2000)