Consumer confidence dipped in the fourth quarter as the post-Brexit collapse of the pound started to weigh on households.
Deloitte's latest Consumer Tracker showed that overall consumer confidence dropped to minus 6% between September and December, from minus 5% in the previous quarter.
While essentials spending grew from a balance of 5% to 12%, and discretionary spending inched higher from minus 2% to 0%, Deloitte said the "upbeat" results may not continue in 2017.
The survey - which polled 3,000 UK consumers between December 31 and January 2 - found that confidence in disposable income dropped in the final three months of the year from minus 12% to minus 14%.
Deloitte said it could mark the start of pressure on household spending.
Ian Stewart, chief economist at Deloitte, warned: "The New Year sees the arrival of headwinds that may challenge the current consumer-friendly economic conditions.
"Falling confidence about disposable income may be a sign that we are seeing the start of a squeeze on household incomes.
"Rising inflation, largely driven by the weakening pound in recent months, will also put pressure on real incomes and consumer spending in 2017."
Britain's Consumer Price Index measure of inflation rose to a two-and-a-half year high of 1.6% in December, and is expected to rise further over the coming year as companies start to see their hedging positions unwind.
The majority of Britain's retailers have so far dodged the impacts of the currency's collapse through hedging practices that include buying dollars in advance. But they may be forced to raise prices as those positions expire.
The pound is trading nearly 16% lower against the US dollar versus its pre-referendum peak, and 10% lower against the euro.
Confidence in job security stayed steady at minus 4% in the fourth quarter, while an annual measure of retail sales value growth rose from minus 1.1% in December 2015 to a positive reading of 7.1% at the end of 2016.
Sentiment among younger workers aged 18 to 34 reached a record high in the fourth quarter thanks to rising confidence in disposable income, debt, job security, job opportunities and career progression.