SIOG1650 - Introduction and organisation: recording information: corresponding with taxpayers direct
There are specific situations where you must write direct to the taxpayer because the item in question has to be served on the individual or entity. Otherwise you may correspond with an agent or adviser as long as HMRC holds an appropriate authority from the taxpayer. Where you send a letter direct to a taxpayer, you should send a copy to any adviser or agent for whom an authority is held. Particular care should be taken to check for the existence of authorities where your enquiries involve numerous entities and individuals.