The first details of the new Mini Convertible have been released ahead of the cabriolet’s launch next year.

BMW has placed a large emphasis on the Mini’s green credentials with the convertible’s emissions slashed by 23 per cent without compromising performance.

Available as a 1.6-litre Cooper or turbocharged Cooper S model, the Minis will develop 120bhp and 175bhp respectively and both use a six-speed manual gearbox.

This enables the Cooper S to accelerate from 0-62mph in 7.4 seconds and reach 138mph while the Cooper manages 9.8 seconds and 123mph.

However, it’s the green measures which are most impressive with the Cooper capable of 49.6mpg (up from 38.7mpg) while CO2 emissions have been slashed from 174g/km to 137g/km.

The Cooper S has also benefitted from BMW’s EfficientDynamics programme which includes stop-start technology and brake energy regeneration with emissions down 23 per cent to 153g/km and fuel economy up 10.1mpg to 44.1mpg.

BMW has fitted the Mini Convertible with a canvas roof which can fully retracted or closed in 15 seconds and can be operated at speeds of up to 20mph.

To prevent ‘scuttle shake’, which is where the car’s composure is reduced with the roof removed, the Mini Convertible’s body structure has been strengthened and stiffened. Despite this, the Mini weighs 10kg less. 

For the first time, the Mini Convertible will have air-conditioning as standard, but as usual there will be plenty of optional extras available.

This includes the ‘Openometer’, which records the time spent by the driver with the roof down.

With the roof up, the Mini’s boot has a volume of 170-litres – a 5- litre increase – and is reduced to 125-litres when driving with the roof down.

The Mini Convertible goes on sale on March 29, 2009 with the Cooper costing £15,995 and Cooper S £18,995.