One million pounds’ worth of stock from a new high-end underwear brand has been stolen in a lorry heist just days before the label’s launch.

The new label Les Girls Les Boys, established by Agent Provocateur founder Serena Rees, is due to launch on 1 September. The stock was stolen while being transported to a warehouse in Leeds on 20 August.

South Yorkshire police have launched an investigation, and the brand has offered a cash reward for any information which leads to a prosecution. The company did not comment other than to confirm the facts of the theft.

Police said the side curtains of the lorry had been cut open to steal the stock, but the fact that the garments were not yet on the market would make it easier to track them down.

Les Girls Les Boys, a unisex “collection of modern intimates and layers”, is launching with a range of underwear, T-shirts, pyjamas, hoodies and jogging bottoms, with prices ranging from £20 to £120.

Speaking when the brand was announced in May, Rees said there was a need for “an openminded brand with a more diverse story to tell”, explaining that she had been inspired by the way her children shared each other’s clothes.

Rees founded Agent Provocateur with her then husband, Joseph Corré, the son of designer Vivienne Westwood, in 1994. Following the couple’s divorce, the company was bought by a private equity firm for £60m in November 2007. In March this year it was bought by Four Holdings, which is linked to Sports Direct owner Mike Ashley, after it was placed into administration.

A spokesperson for South Yorkshire police said: “At 7.56am on 19 August, we received a report of a theft from an articulated lorry which had been parked up near the Dodworth business park in Barnsley. The driver of the lorry reported to us that the side curtains on the lorry had been cut open and that a quantity of garments had been stolen from the rear of the vehicle.

“We are now investigating the theft and hope to speak to the driver again to gain more information. We will also try to locate the stolen stock. The fact that the items were not yet on the market will help us to track them down. We are asking anyone who has information to call us on 101.”

The new brand is not the first to fall victim to thieves while in transit. In April several boxes of the coveted Adidas Yeezy Boost 350 V2 trainers, designed by Kanye West, were stolen from a truck delivering the shoes to the Rezet store in Copenhagen, Denmark.

