The Wine Merchant Magazine runs an annual competition where a selected panel of independent merchants blind-taste their way through more than 1,000 wines. The result is a great list of wines (also available as a magazine supplement) which arguably is the best of the best.
Here are the value wines from the list:
Best Value Red Trophy: Zuccardi Los Olivos Malbec, Mendoza 2020 (£12.90, Hatch Mansfield)
Best Value White Trophy: Wildeberg Wild House Chenin Blanc, Western Cape 2022 (£8.99, Boutinot)
Best Value Sparkling Trophy: Global Wines Portugal Cabriz Espumante Brut 2017 (£16.50 Marta Vine)
These wines are stocked by many independent specialist online and physical stores. The best way to find them is to do a Google search.