21. Maxibrite briquettes, manufactured by Maxibrite Limited at Llantrisant, Rhondda Cynon Taff, which–
(a)comprise anthracite fines (as to approximately 84 per cent of the total weight), petroleum coke (as to approximately 12 per cent of the total weight) and starch as binder (as to the remaining weight);
(b)were manufactured from those constituents by a process involving roll-pressing and heat treatment at 250°C;
(c)are cushion-shaped briquettes marked with the letter “M”;
(d)have an average weight of 35 grammes per briquette; and
(e)have a sulphur content not exceeding 2 per cent of the total weight.