25The price at which scheme shares may be acquired by the exercise of a right obtained under the scheme—
(a)must be stated at the time the right is obtained, and
(b)must not be manifestly less than 90 per cent. of the market value of shares of the same class at that time or, if the Board and the grantor agree in writing, at such earlier time or times as may be provided in the agreement,
but the scheme may provide for such variation of the price as may be necessary to take account of any variation in the share capital of which the scheme shares form part.