Mercedes is applying the finishing touches to its all-new SLK as the popular folding hard-top roadster enters its latter stages of development at the Nurburgring.

This test car is the second lightly disguised SLK to be spotted in the past month. Although at first glance it appears similar to its predecessor, the new SLK features overhauled styling dominated at the front by a large oval shaped grille inspired by the look of the new CLS revealed at last week's Paris motor show.

Dimensionally, the two-seater new roadster has grown, but not by much. Length is up by 31mm at 4131mm, width extends by 33mm to 1808mm and height is up by a scant 9mm at 1304mm – all of which has served to liberate greater interior accommodation and boot space.

It’s underneath the aluminium and steel body, though, where Mercedes-Benz concentrated much of its development work. “We wanted to give the SLK a more sporting flavor without compromising its inherent comfort,” project leader Jürgen Weissinger told Autocar last month.

Among the chassis developments are wider tracks and variable damping control that will be offered as part of an optional agility package.

Read the full story on the next SLK, including more spy pics

Power for the new SLK comes in the form of three petrol engines and, for the first time, a single diesel. Kicking off proceedings is a base SLK200 CGI model running a turbocharged 1.8-litre four-cylinder direct-injection unit with 184bhp and 199lb ft of torque.

It will be joined by the mid-range SLK250 CGI using the same basic engine as its more affordable sibling but tuned to deliver a sturdier 204bhp and and 229lb ft. Positioned above it will be the SLK350 CGI, which adopts the company’s new 3.5-litre V6 direct-injection engine, as recently unveiled in the S-class.

For the first time there will also be a diesel in the form of the SLK250 CDI, although it is unclear whether it will be sold from the outset. It uses Mercedes’ 2.2-litre four-cylinder common-rail diesel engine delivering 204bhp and 369lb ft.

It is set to go on sale in the UK shortly after a planned unveiling at next year’s Geneva motor show.