IFM09748 - Administrative requirements: Provision of information to HMRC: form and manner of providing accounting period information
HMRC may publish a notice under Regulation 39 specifying the form and manner in which notices, applications and information under Part 2 of the regulations must be given or made to HMRC. HMRC requires the relevant RIF notifications and accounting period information to be submitted electronically. The notice specifying that requirement, and details of how to comply with it, are set out on the relevant GOV.UK page.