The Council Tax (Reductions for Annexes) (England) Regulations 2013
Section 13 of the Local Government Finance Act 1992 makes provision for reduced amounts of council tax to be payable if certain conditions prescribed by the Secretary of State are fulfilled. These Regulations relate to England and prescribe a 50% reduction in the amount of council tax payable (on top of any discounts under sections 11 or 11A and/ or any premiums under section 11B) for people living in annexes provided they are related to the person liable to pay the council tax of the main dwelling (or the person who would be so liable were it not for an exemption or 100% discount or reduction), and for people living in dwellings with annexes which are unoccupied provided they are using those annexes as part of their main residence.