M140i vs 340i vs 540i — The BMW B58 Used-Car Buying Guide

Three used BMWs, one award-winning engine family — but three completely different ownership decisions. In this The Bonnet Files investigation we compare the BMW M140i, 340i F30 and 540i G30 on Britain's used market. We examine original UK list prices, October 2026 used asking-price benchmarks, the B58's genuine Wards recognition, cooling-system inspection points, modifications, insurance, servicing history and the checks worth making before buying. Our verdict distinguishes the best enthusiast's hatchback, the strongest value luxury saloon and the most rounded everyday choice. No engine award can replace inspecting the individual car. UK price references: BMW UK PressClub launch material and AutoUncle UK October 2026 listings. Reliability and inspection research: PistonHeads UK, UK specialists, Auto Express, BMW UK recall lookup and GOV.UK MOT history. Advertised prices are not completed sales and can change. Not every recall or defect applies to every VIN. Which would you choose — M140i, 340i or 540i? Share your actual UK ownership experience below, including mileage and repairs. Before you pay for the badge, open the file.