Sch 1 para 8
(1) Where— (a) a person has a progressive condition (such as cancer, multiple sclerosis or muscular dystrophy or HIV infection ), (b) as a result of that condition, he has an impairment which has (or had) an effect on his ability to carry out normal day-to-day activities, but (c) that effect is not (or was not) a substantial adverse effect, he shall be taken to have an impairment which has such a substantial adverse effect if the condition is likely to result in his having such an impairment. (2) Regulations may make provision, for the purposes of this paragraph— (a) for conditions of a prescribed description to be treated as being progressive; (b) for conditions of a prescribed description to be treated as not being progressive.