Not to steal from Robin's excellent work, you can see how much it's been (low carbon/renewables generation) over the last twelve months at https://app.electricitymaps.com/map/zone/GB/12mo/monthly (~56% renewables, ~73% low carbon)
(Robin, if there is a way to see this on your site, I could not find it, my apologies!)
(Robin, if there is a way to see this on your site, I could not find it, my apologies!)