The argument for the second interconnector rests on an assumption that has not been true in any of the last four winters.
The claim
Proponents argue that 1.4 GW of additional import capacity removes the need for the two remaining peaking plants, on the basis that the continental price is reliably below the domestic one at peak.
What the data says
In the four most recent winters, the hours in which the domestic system was tightest were also the hours in which the continental system was tightest. The correlation is not incidental — both are driven by the same anticyclonic conditions, which suppress wind across the whole basin at once.
On the eleven tightest evenings of the last four winters, the interconnectors were exporting on six of them.