The engine also switches seamlessly between running on four cylinders and on two cylinders under light loads, the only way you can tell is from a read out on the instrument cluster telling you that you're in two cylinder mode.
On our 200-mile test route taking in mainly motorway running, an indicated 47mpg was returned. Some way off the official 60.1mpg figure, then, but very impressive indeed for an engine with these performance figures.
Elsewhere, it’s more of the same Leon ST dynamics we’ve become accustomed to: a compliant ride, tidy handling and steering that is precise but lacks feel.
Standard equipment is impressive in the FR, and it also looks the part inside and out with its own bespoke sporty bumpers, twin chrome exhaust pipes, tinted rear glass, sports seats, racy interior trim and FR badging.
Our test car was equipped with an optional set of £380 18-inch alloys, which look smart and ruin neither the bank balance or ride quality. Alloys of 17 inches in diameter are standard.
Should I buy one?
Equipped with this new engine, the Leon ST is a car that ticks many boxes - space, performance, economy and a decent drive among them - in an increasingly competitive class, and one that should be on our shopping list.
A Ford Focus offers a better drive, a VW Golf an extra layer of polish and a Skoda Octavia more space, but the Leon’s appeal lies in the way it blends so many qualities, and trumps anything in the class on style.
Seat Leon ST FR 1.4 TSI ACT 150 PS
Price £20,995; 0-62mph 7.9sec; Top speed 134mph; Economy 60.1mpg; CO2 109g/km; Kerb weight 1277kg; Engine 4cyls, 1395cc, turbocharged; Power 148bhp at 5000-6000rpm; Torque 184lb ft at 1500-3000rpm; Gearbox 6-speed manual