7. A modification is a permitted modification if—
(a)the modification provides for the provision of services in addition to the services already provided for in the public service contract,
(b)using a different operator would result in the provision of services that are different from, or incompatible with, those already provided for in the public service contract,
(c)the competent authority considers that the difference or incompatibility would result in—
(i)disproportionate technical difficulties in operation or maintenance or other significant inconvenience, and
(ii)the substantial duplication of costs for the authority, and
(d)the modification would not increase the estimated value of the public service contract by more than 50%.