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HMRC internal manual

Inheritance Tax Manual

Communications: Use of fax machines: what priority to give faxed documents

You should deal with any documents received by fax with the correct degree of urgency. You should not let correspondence sent by fax interfere with your priorities (IHTM02084) for dealing with other cases unless there is good reason.

If you receive correspondence by fax it does not necessarily mean that a reply should also be sent by fax