All-new hatchback ousted in leaked images, showing off its refreshed design. Expect an official debut at the Frankfurt motor show in September.

The new-generation BMW 1 Series has been leaked online, ahead of an anticipated reveal later this year.

Posted by BimmerFile, the pair of images show the front and rear of the all-new hatchback, in flagship M135i xDrive form.

In terms of the overall design there aren't too many surprises, with the exterior blending elements from across BMW's newest line-up.

Up front there's a strong resemblance to the X1 and X2 crossovers the 1 Series will share its UKL front-drive architecture with, while the angular rear with slim LED tail-lights shows strong family links to the new 3 Series and 8 Series, albeit with the hatchback rump.

Expect the core range to look a lot more sedate than the M Performance variant you see here, complete with an aggressive bodykit and dual exhaust outlets.

We can't see the wheels from these angles, but we expect the rims to range from 16 to 19 inches depending on specifciation.

As for powertrains, we know the M135i xDrive will be powered by a high-output 2.0-litre turbo four shared with the X2 M35i xDrive – a key difference between the new generation and the current inline six-powered model.

Outputs will likely mirror that of its crossover sibling, meaning the M135i xDrive should make 225kW and 450Nm of torque. BMW says this engine is the most powerful production four-cylinder motor its ever made.

Further changes will be made under the skin, where the new 1 Series will make the switch from rear- to front-wheels drive, with xDrive all-wheel drive available depending on variant and market.

We don't have any undisguised images of the interior, but expect a slightly shrunken version of the cabin from the new 3 Series.

That means the company's latest BMW OS7.0 infotainment and navigation software, all the latest driver assistance and active safety systems, and a far more upmarket ambience afforded by more modern design and higher quality materials throughout.

It's believed the all-new 1 Series will make its official debut at the 2019 Frankfurt motor show in September. Stay tuned to CarAdvice for all the latest.