The Board may at any time revoke any such certificate if it appears to the Board that the person to whom it relates is not a fit and proper person to perform the relevant functions.

Where the Board determine to revoke any such certificate, they shall serve a notice on the person to whom it relates stating that the certificate is revoked as from the end of the period of twenty-one days from the date of service of the notice; and the revocation shall take effect at the end of that period.