Smartphones will have a key role to play in the UK's shopping habits this Christmas, with new forecasts suggesting GBP3.5bn (US5.6bn) worth of retail sales will be purchased on or influenced by the devices.

Business advisory firm Deloitte says shoppers will use their smartphones to research prices, store Christmas shopping lists, engage with friends and family using social media - and increasingly to make payments for goods.

Its research suggests around GBP3.2bn of in-store Christmas sales will be influenced by smartphones, with another GBP330m bought directly through the devices. A further GBP500m in sales will be made through tablets.

Deloitte also forecasts another strong year for online retail, with sales increasing this Christmas by 17% - outstripping a 1% rise in total UK retail sales.

"We remain cautious on the long-term outlook for UK retail, but there are more reasons to be optimistic than pessimistic this Christmas," said Ian Geddes, UK head of retail at Deloitte.

"Consumer confidence has gradually improved over the course of the year and despite the recent increase in inflation, it is much lower than it was 12 months ago, easing the pressure on households. "Whilst it is not certain whether this will translate into higher spending, with consumers continuing to show a desire to save, we believe it will be enough to generate modest growth."

He adds that rising food prices are likely to weigh on general merchandise sales, which are seen as "flat at best and very possibly experience a slight fall as consumers decide to save the Christmas dinner."

But he adds: "Shoppers are responding to those retailers that combine the right products with exceptional customer service across all channels, dynamic and exciting online and mobile sites and a brand that they want to be associated with and invest in."

The business advisory firm adds that while 10% of in-store sales will be influenced by smartphones in December this year, by 2016 this figure will be as high as 18% for the full year, equivalent to GBP43bn of sales.