12Paragraph 4 above does not apply—
(a)to dismissal from employment under a contract for a fixed term of two years or more, where the contract was made before 28th February 1972 and is not a contract of apprenticeship, and the dismissal consists only of the expiry of that term without its being renewed, or
(b)to dismissal from employment under a contract for a fixed term of two years or more, where the dismissal consists only of the expiry of that term without its being renewed, if before the term so expires the employee has agreed in writing to exclude any claim in respect of rights under that paragraph in relation to that contract.