While it's true that the UK doesn't have nodal electricity pricing per unit of energy (and Ofgem, the regulator, agrees that this would have benefits[0]) I'm not sure we'd be in much of a different position if we had.
We haven't seen particularly rapidly growing demand as energy efficiency improvements and the closure of heavy industry has offset the general increase in energy intensity which happens over time as economies grow.
It's also not like there is no locational signal in the current system - the costs which large generators and large consumers pay to use the transmission network do depend in part on where they are connected and how much of the peak network capacity need they are responsible for (so called "triad charges").
There are also significant revenue incentives for building embedded (ie distribution-connected) generation.
Ultimately it's hard to avoid the fact that we closed down old reliable coal and gas generation without having the right replacements in place. Governments of all political stripes didn't want to take decisions (eg on new nuclear especially but also things like pumped storage hydro) because it was easier to pretend these changes were cost free.
0. https://www.ofgem.gov.uk/publications/assessment-locational-...