Today’s numbers are up from the 2.6% level of inflation, which was recorded in the previous figures for both July and June.
The bigger-than-expected rise in inflation comes ahead of the Bank of England's next announcement on interest rates, which is due on Thursday.
Clothing and footwear prices had the biggest impact on the inflation rate last month, according to the ONS.
They climbed 4.6% year-on-year, their highest level since records began, partly because of rising import costs for retailers.
TUC general secretary Frances O’Grady said: “The cost of living squeeze continues, with rising inflation outpacing wages."
She warned against “a pick and mix approach” to public sector pay after reports emerged that the government was considering scrapping the 1% public sector pay cap for prison and police officers.
A Treasury spokesperson said: “We know some families have concerns with their day to day cost of living.
“That’s why we are boosting take home pay with tax cuts for over 30 million people and a National Living Wage that is giving the lowest earners their fastest pay rise for 20 years.”
Labour accused the government of failing the public on living standards.
Peter Dowd, Labour’s shadow chief secretary to the Treasury, said: “The continued rise in inflation will come as further bad news for working families; who after 7 years of Tory economic failure have seen their wages fail to keep up with prices.”
