Britain's annual rate of consumer price inflation rose for the first time in 10 months in December, increasing to 4% from a more-than-two-year low 3.9% in November, official figures unexpectedly showed today.
A rise in tobacco duty lay behind the increase, the ONS said.
A Reuters poll of economists had pointed to a fall in inflation to 3.8%.
The data, which follows bigger-than-expected falls in inflation in recent months, potentially adding to concerns at the Bank of England, which raised interest rates to a 15-year high of 5.25% in August.
The rise in Britain's inflation rate followed increases seen in the euro zone and US in December.
Today's figures may dampen financial markets' conviction that the Bank of England will start cutting interest rates in May this year.
The Bank of England forecast in November that it would take until late 2025 to return inflation to its 2% target, but many economists now think this could happen as soon as April or May this year due partly to a slide in wholesale gas prices.
Surging gas prices following Russia's invasion of Ukraine pushed British inflation to a 41-year high of 11.1% in October 2022, adding significantly to existing inflation pressures from supply chain difficulties following the Covid-19 pandemic.
Today's figures showed that core inflation - which excludes volatile food, energy, alcohol and tobacco prices - was 5.1% in December, the same rate as November.
Services inflation increased to 6.4% in December from 6.3% in November.
The Bank of England looks at both core CPI and services inflation as a better guide to underlying price pressures in the economy, especially those caused by rapid wage growth.
Figures yesterday showed average weekly earnings excluding bonuses rose by an annual 6.6% in the three months to the end of November - the slowest increase in nearly a year but roughly double the pace the Bank of England views as consistent with getting inflation back sustainably to 2%.
