Demand was on a constant down trends. From PCs, servers over light bulbs to electric based heating (heat pumps and IR heat lamps instead of "direct" electric heating + better insulation) everything has got _way_ more efficient. But also a lot of high energy need industry has moved of from the UK (or most 1st world countries) for decades by now.
A short (not proper) lookup show that even if you where to replace _all_ cars in the UK with electric cars the total need for that would be 30TWh/y while the UK produces ~322TWh/y so less then a 10% increase (in relation to production, not consumption).
The only thing which has caused a mayor hickup more or less all countries long term plan for electricity production is AI.
But not because GPGPU compute is that inefficient, it has gotten way more efficient. But instead because of how insanely much compute AI needs.