There's a project that's planning solar power generation in Morocco and a cable to the UK. That'll be a fairly long cable. https://en.wikipedia.org/wiki/Xlinks_Morocco-UK_Power_Projec.... Though no idea how realistic this is, it seems a bit like a new electric car company website that only has a prototype. Meaning, it seems that project seems to not escape the planning stage.
There's already a lot of cables between the UK and other countries, e.g. Norway and France. Though those aren't that long in comparison to something connecting to the UK.
EU is trying to tie all the various grids of the various countries together. There are loads of initiatives around that. Aside from that the Southern EU countries are trying to connect their grids to North Africa. Though again, that's not a huge distance to cover.