So the Gateshead scheme appears to be up-and-running since March this year: https://www2.groundstability.com/major-grant-to-connect-gateshead-homes-to-coal-authority-mine-water-energy-scheme/

There’s a similar scheme already in place in the Netherlands: https://www.construction21.org/articles/h/from-flooded-mines-to-circular-district-heating.html

And also In Spain: https://www.thinkgeoenergy.com/turning-coal-mines-in-the-region-of-asturias-in-spain-to-sources-of-geothermal-heating-and-cooling/amp/

So I agree the article is a bit light on details, but it’s definitely happening to one degree or another.