(1) Except as otherwise provided in these Regulations, the volume of allowances to be auctioned in any calendar year must be AC - (AFA + IC + RFS + NER + BF) + T, where -

(a) AC for the calendar year is the base for that year determined in accordance with paragraph (10)(a) multiplied by -

(i) in the case of a calendar year up to and including 2025, the 2021-2025 hospital and small emitter reduction factor calculated in accordance with article 21(2) of the Trading Scheme Order [The Greenhouse Gas Emissions Trading Scheme Order 2020 (S.I. 2020/1265, amended by S.I. 2020/1557, S.I. 2021/1455, 2022/454, 2022/1173, 2022/1336 and (with effect from 1st January 2024) 2023/850). "Trading Scheme Order" is defined in regulation 2(1) of S.I. 2021/484.];

(ii) in the case of a calendar year from 2026 up to and including 2030, the 2026-2030 hospital and small emitter reduction factor calculated in accordance with article 21(3) of the Trading Scheme Order;

(b) in relation to a calendar year corresponding to a scheme year ["Scheme year" and "2021-2025 allocation period" are defined in in article 4(1) of S.I. 2020/1265. Regulation 2(3) of S.I. 2021/484 provides that terms used in both S.I. 2021/484 and S.I. 2020/1265 and not defined in the former have the same meaning as in the latter.] in the 2021-2025 allocation period, "AFA" is -