BMW will break the 120g/km CO2 emissions barrier and top the 60mpg mark with the most efficient version of the 5-series, the 520d ED, which arrives in the UK this September.

Full details of BMW's third super-eco ED car, after the current 320d ED and the recently announced 116d ED, will be revealed at the end of June. Based on the 520d SE, the new 5-series ED model will only be available as a saloon with a manual gearbox. However, this means the car will have an official mpg figure of 62.8mpg, some 5mpg higher than the similarly powerful 520d.

The CO2 figure will come in at 119g/km, which puts the car in the lowest benefit-in-kind band for diesels this year at 18%. This is the same band as the regular 520d, but with the tightening BIK bands, the next tax year (2012/13) will see the 129g/km 520d SE move to band 19% while the 520d ED will drop to 17%. The CO2 and mpg figures put the BMW back ahead of rival cars from Audi and Mercedes.

Specification will be similar to that of the SE car, however the ED model will be fitted with 16-inch alloy wheels as standard for ultimate economy, but with the no-cost option of an upgrade to 17-inch alloys. Performance, too, will be very similar to the standard 520d with the ED having a 0-62mph time of 8.2 seconds, just 0.1 seconds slower than the 520d.