if the UK looked like routinely producing multiple-gigawatt power surpluses on windy days, then you would need to justify the cost of the interconnect and of the pumps. It could run the other way, of course, on cold windless days.

That cost might be a bit high if it's only a matter of extreme peaks and troughs, a few hundred hours a year? But if the Scandi hydro pumped storage benefited all Europe, that would mutualise the costs.

Would UK excess wind be characterised by season? Mostly in winter? In that case it wouldn't seem to be a good fit for longer-term smoothing: dams already full I suppose.

_{It is rightly acknowledged that people of faith have no monopoly of virtue - Queen Elizabeth II}