Watch: First look at John Lewis Christmas advert as retailer releases sneak preview

John Lewis has released an early hint of its Christmas advert with a new campaign centred on its recently-revived "Never Knowingly Undersold" price pledge.

The "through the decades" ad is the first in a three-part campaign for the all-important retail "Golden Quarter", which will culminate with the department store's highly-anticipated Christmas spot.

The first advert features archive footage and focuses on a single store window changing over a century as it is dressed and redressed with products such as fashions of the roaring 1920s and a toaster so innovative that it took centre stage in 1925.

A version of Paul Simon’s "I Know What I Know" - sung by Laura Mvula - provides the soundtrack.