Significant changes were made to the section 21 regime by the implementation of the Deregulation Act 2015 (DA 2015) which, inter alia, made amendments to the Housing Act 1988 (HA 1988) and Housing Act 2004, and the Assured Shorthold Tenancy Notices and Prescribed Requirements (England) Regulations 2015 (ASTN Regs 2015), SI 2015/1646. DA 2015, s 37 introduced into section 21 the power for regulations to prescribe the form of a section 21 notice, with the ASTN Regs 2015, SI 2015/1646 being made to this effect. ASTN Regs 2015, SI 2015/1646, reg 1 provides that the regulations apply in relation to an assured shorthold tenancy (AST) of a dwelling-house in England granted on or after 1 October 2015, but do not apply to one which came into being