The Mercedes CLA will cost from 24,355 and order books are open now.
Two engines and two trims are available from launch, with more engines expected to follow later.
The CLA180 uses a 120bhp 1.6-litre four-cylinder petrol engine, which takes it from 0-62mph in 9.3 seconds. The diesel-powered CLA220 CDI produces 168bhp and gets from 0-62mph in 8.2 seconds.
Petrol cars are fitted with a six-speed manual gearbox, while the diesel gets a seven-speed automatic 'box.
The CLA180 does an average of 50.4mpg and emits 130g/km of CO2, while the 220 CDI averages 62.8mpg and has CO2 emissions of 117g/km.
Two trims are available: Sport and AMG Sport. Standard equipment for both includes climate control, Bluetooth, twin stainless steel tailpipes and automatic wipers.
Sport cars also get comfort suspension, 18-inch alloys, sports seats, a black grille and a multi-function sports steering wheel.
AMG Sport adds sports suspension, 18-inch AMG alloys, an AMG styling package, privacy glass and bi-xenon headlights.
The CLA180 Sport starts at 24,355, while the CLA220 CDI costs from 29,355. AMG Sport trim costs an extra 2200 regardless of engine choice.
UK deliveries will start in June. Mercedes is yet to confirm more engines for the CLA but expect a full AMG version with four-wheel drive to follow later.