UK HMRC has published guidance on reporting cross-border arrangements under the new Mandatory Disclosure Rules. The new rules were recently introduced through the International Tax Enforcement (Disclosable Arrangements) Regulations 2023, which are based on the OECD's Model Mandatory Disclosure Rules for CRS Avoidance Arrangements and Opaque Offshore Structures (previous coverage). Reporting under the new rules will not be available until they enter into force on 28 March 2023. Until then, th…