12. In a case to which paragraph 3 of Schedule 2 applies, the day of incapacity for work mentioned in sub-paragraph (1)(b) of that paragraph shall not be, or form part of, a period of interruption of employment where it is a day which, by virtue of section 17(1) or (2) of the Social Security Act 1975 or any regulations made thereunder, is not to be treated as a day of incapacity for work.