Subject to the following provisions of this section, the Secretary of State may at any time vary a merger reference made under section 69(4) of this Act.

A merger reference made under section 69(4) of this Act shall not be so varied that it ceases to be a reference limited in accordance with that subsection.

Without prejudice to the powers of the Secretary of State under section 70 of this Act, a merger reference shall not be varied so as to specify a period within which a report on the reference is to be made which is different from the period specified in the reference in accordance with that section.