The likes of Red Bull, Unilever, Heineken and Walkers are preparing to unleash an army of mystery shoppers - equipped with a new mobile app - to check the availability, merchandising and promotion of their products.

From Monday, iPhone owners who download the free ‘Roamler’ app will be able to carry out mystery shopping tasks in exchange for cash.

More than 1,000 UK shoppers have already signed up to undertake tasks ranging from checking a supermarket flower display and answering questions about it to photographing a pint of Heineken in a pub to show whether it’s served in a Heineken-branded glass.

The data is then fed back to the supplier and the shopper is paid - £3 and £3.50 respectively in these two instances.

“We can offer brands blanket coverage very quickly, like checking on shelf placement or availability in over 250 supermarkets in one day,” said Roamler co-founder Wiggert de Haan. “And because we take pictures, we offer hard, evidential proof of whether a brand is being promoted as intended. There is a huge opportunity for suppliers to capitalise on this.”

The app was launched in the Netherlands last October. Around 150,000 tasks have been carried out by 5,000 mystery shoppers on behalf of brands including Coca-Cola and Danone

Roamler hoped to build a base of 5,000 to 7,000 UK mystery shoppers to offer “blanket” coverage in the UK, said de Haan.

One reason the app was popular with shoppers was that tasks were tailored to the individual’s location, he added.

“If we have a task which requires something to be checked in a Tesco we can use the iPhone’s celltower location functionality to locate shoppers in the vicinity of a Tesco - and only they will receive a push message containing a task,” he said.