HVDC links are more efficient than terrestrial AC transmission lines over long distances.

Also a lot more expensive. The UK is not big enough for it to make technical sense.

> The UK is not big enough for it to make technical sense.

The UK market maybe not, but the UK could make a truckload of money selling their wind power to France to aid their old, barely running NPPs.

And that is happening. There are multiple cross channel HVDC lines and more on their way. These make perfect sense.

The equipment costs (eg: converter stations) for an HVDC link are more expensive, but by running under the sea you save on a lot of other costs (ie: civil engineering, land acquisition, etc).

Building any new transmission line through densely-populated England is extremely expensive. Even if you can secure the necessary land and wayleaves, nobody wants them running near their house and spoiling the views, so significant segments have to run underground in tunnels, greatly increasing costs.

Besides, the UK is not that small when linking England and Scotland. The proposed Eastern Green Link 2 (EGL2) is 440 km long: there are many existing HVDC connections much shorter than that around the world!

Most of these issues are not technical so I stand by my assessment.

You are absolutely right. Building pylons through much of England means dealing with highly organized NIMBYism - from people who care a lot about their local 'environment' but very little about catastrophic floods or fires in other countries, and highly opportunistic landowners who can name their price for use of their land.

DC links are usually built to better control frequency in grids.

They are expensive things, and typically not something left to popular vote.