2 · 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.4
The correlation is not incidental. Both are driven by the same anticyclonic conditions, which suppress wind across the whole north-western European basin simultaneously and raise heating demand at the same time.
The consequence is that interconnector capacity is least useful precisely when it is most needed. On the eleven tightest evenings of the last four winters, Great Britain was exporting on six.5
This is not an argument against interconnection in general, which has clear value in ordinary conditions. It is an argument against counting interconnector capacity toward a security-of-supply standard that is defined by the tightest hours.