The new rate - expected by economists - signals that CPI inflation has been at least a percentage point above the Bank of England's 2pc target since November 2009.
The retail prices index (RPI) gauge, which includes more housing costs and is the benchmark for many wage deals, rose from 4.8pc in December to 5.1pc, its highest since May.
"This is another kick in the teeth on the inflation front for the Bank of England, albeit slightly less hard than some had feared," said Howard Archer, UK economist at IHS Global Insight. "It maintains pressure on the Bank to retaliate by raising interest rates sooner rather than later."
Alan Clarke, UK economist at BNP Paribas, said Mr King's reference to division on the MPC over the inflation forecast suggested that another dissenter may have joined Martin Weale and Andrew Sentance at the last meeting in voting for a interest rates rise.
In response to Mr King's letter, Chancellor George Osborne said the Coalition's austerity plan will give the MPC "the space it needs to target low inflation?, arguing that easing back on the pace of cuts would make the Bank's job harder by adding to inflationary pressures.
Economists generally expect the Bank to raise interest rates from their record low of 0.5pc late in the year, but investors are betting that the inflation problem means a rise will come significantly earlier, arriving by May.
James Knightley, of ING Bank, said all eyes are now on the Bank's quarterly inflation report published on Wednesday, when it will update its forecasts for growth and prices.
"The general tone of the report and the accompanying press briefing will give us a much better idea as to whether the market fully pricing in a rate hike by May is realistic," he said.
On the latest figures, the ONS said the biggest price rises were in areas such as fuel, cars and eating out. In contrast, clothing acted as a drag on the overal level of inflation, as retailers cut prices in the January sales.
On the month, CPI was up 0.1pc, the first time it has risen between December and January since records began. CPI typically falls in January due to post-Christmas discounting.
Looking ahead, the inflation rate should keep rising as the oil price and the costs of other commodities climb further and companies continue to pass on the impact of the VAT rise to their customers.
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