CMP306: Align annual connection charge rate of return at CUSC 14.3.21 to price control cost of capital

The purpose of this modification is to align the rate of return applied to the net asset value of connection points in the calculation of annual connection charges (as set out at paragraph 14.3.21 of the Connection Charging Methodology) to the pre-tax cost of capital in the price control of the Relevant Transmission Licensee (plus a margin of 1.5 percentage points in the case of MEA-linked assets).  This will improve the cost reflectivity of the charges, since the return on capital will equal the Authority’s most recent assessment of that cost for the Relevant Transmission Licensee.