This part of GOV.UK is being rebuilt – find out what beta means

HMRC internal manual

Inheritance Tax Manual

Communications: Use of fax machines: documents that are unacceptable if sent by fax

Any document which requires the signature(s) of the liable people must bear the actual signature(s), so copies of these documents cannot be sent by fax. You should bear this in mind if a customer asks you to accept a document by fax.

In very urgent cases it may be possible for the customer to fax copies so a matter can be considered whilst the originals are being forwarded by post.