Research among 300 European retailers by MasterCard finds that by 2020, 43% of the sample believe the smartphone will become the most important channel - overtaking stores, PCs, call centres and direct mail. Forty-one percent of retailers envisage they will provide mobile points-of-sale in-store by 2020, whilst 33% will provide self-service kiosks and 35% will use location-based technologies to attract new sales.

According to Deloitte's study, six percent of in-store retail sales in the UK are already being influenced by smartphone use, equivalent to £15.2bn of sales this year. This is almost double the value of direct purchases made through mobiles, which are estimated at around £8bn in 2012.

By 2016, more than 80% of consumers are expected to own a smartphone and Deloitte estimates that between 15% and 18% of in-store sales will be smartphone-influenced, equivalent to £35-43bn.

However, whilst 64% of smartphone owners are estimated to have used their device to make a bank payment or pay a bill, just one percent have used their phone to make an in-store payment.

This may soon change, as more retail terminals are converted for the 'tap-and-go' generation. MasterCard's research finds that over the course of the next year, 44% of the retailers polled plan to offer contactless payment technologies in-store, voting this the single most important area for short-term investment.

Colin Jeffrey, head of multichannel retail at Deloitte Digital, says: "We would expect smartphones to increasingly be used as a transactional device in the future. The increased adoption of contactless payment technology will act to accelerate the influence of mobile. Retailers need to plan for a world where banks of till points are no longer required and prepare to fully exploit the opportunities that mobile presents."