UK core inflation, which excludes normally more volatile factors such as food and fuel, rose to a 31-year high last month.
The core consumer price index for May was up 7.1% on a year ago, climbing from 6.8% in April, which surprised economists, who expected it to remain unchanged.
Core CPI rose 0.8% month-on-month.
The headline CPI rate also surprised as it held steady at 8.7%, when it had been expected to ease to 8.4% by economists and 8.3% by the Bank of England.
Services prices rose 0.8% month-on-month, pushing up the year-onyear services CPI rate to 7.4% from 6.9% in April.