A recent article on Sky concluded that the under rating of power lines across the Scottish border meant that it was expensive and pointless in connect more 

wind generators in Scotland as that already the power generated could not be transmitted further south where it was needed.

https://news.sky.com/story/britons-paying-hundreds-of-millions-to-turn-off-wind-turbines-as-network-cant-handle-the-power-they-make-on-the-windiest-days-12822156?fbclid=IwAR3vfPknEgAf6pxK934zG0P7Mia18wfSdUvsI8kt9qVfO52p3IQz6COe__U  

The nat grid have at least a100 foot servitude for the existing  line so immediately they must build an extra 2  400kV quad lines one each side of the existing line. There is no time for worrying about planning consents and the government should insist on the grid starting immediately and offer to pay all pre-ordering costs upfront to avoid delays. 

The pipe dream of zero carbon power station emissions by 2050 can certainly not be achieved without serious investment in the grid and nuclear power right away.