Mercedes-Benz will launch a 74g/km version of the S-Class in 2014, but a decision to introduce it in the UK has not yet been made.

The plug-in hybrid would qualify for a discount on the London congestion charge as well as the lowest rate currently available for BIK tax.

However, as the threshold is set at 75g/km for both incentives, Mercedes-Benz would have to ensure that CO2 does not increase for homologation to right-hand drive markets to maintain its appeal.

The new S-Class will arrive in the UK in October with the diesel S350 Bluetec and petrol S500 as well as a petrol-fuelled S400 hybrid. In March 2014 the S300 Bluetec hybrid will arrive, with CO2 emissions of 115g/km.

The S400 hybrid has competitive CO2 emissions with the BMW ActiveHybrid 7 and Audi A8 Hybrid, but the S300 Bluetec would be class-leading. However all versions would still be liable for the full London congestion charge.

But Mercedes-Benz will also launch the S500 Plug-in Hybrid in 2014, and Mercedes-Benz officials in the UK are hoping the ultra-low CO2 model will be introduced here.

The S500 Plug-in Hybrid would offer a short range of zero-emissions driving, but also have a petrol engine to ensure a longer travelling range if required.

The model, which would be priced at the top end of the S-Class range, has slightly reduced luggage space compared with other variants because of the room needed to store the battery.

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