1. North-south links in the UK are already fully utilised. There are more in works and plans but not sure it’s enough to meet even existing demand. 2. Transmission losses are substantial.
Transmission in this sense does not include distribution losses (by the DNOs, at lower voltages). 8% in your link.
The UK government is now touting datacentre sites with better access to the national grid (transmission network) to avoid the issues inherent in the distribution networks. E.g. Culham which had a grid connection to power the JET fusion experiments.