John Lewis is relaunching its ‘Never Knowingly Undersold’ commitment after a two-year hiatus, showcasing the move with a celebratory new brand campaign starring actor Samantha Morton and singer Laura Mvula.

The new campaign, which will make its debut on 19 September, has been described by John Lewis as its “biggest ever” campaign, and will honour 100 years of the price guarantee as it “kick-starts” the brand for the next 100 years.

The retailer initially scrapped the price guarantee due to what it described as “complications” due to people increasingly shopping online.

Following a £multi-million investment and improved price promise, the updated initiative will be using AI and machine learning to check prices at 25 online and high street brands including M&S, Next, Boots and AO.com.

Starting next Monday (9 September), if the price is lower at any of those retailers it will be matched at John Lewis. Customers will also be able to get the difference refunded back if they find their purchase cheaper at one of those brands within seven days.

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“One hundred years ago John Spedan Lewis created Britain’s most innovative and famous brand mantra,” said chief executive Nish Kankiwala.

“It defines why John Lewis is so special, and its unique position in the retail landscape.

“Today, we’re kick-starting our brand for the next 100 years, the perfect fusion of heritage and British eccentricity blended with radical relevance for the modern customer.”

Describing the move as a “significant and critical milestone in the modernisation of John Lewis customer proposition”, the partnership said the return of the price promise campaign is further evidence of the “retail-focused transformation” of the partnership.