The Markit/CIPS services purchasing managers' index survey for February fell more than expected to a five-month low of 53.3 from 54.5 the month before.
The market had been expecting a smaller decline to 54.1, with any reading above 50 indicating growth.
As a result of the services slowdown, the composite PMI for the UK economy slipped to 53.8 for February from 55.4, again short of the estimated 55.6.
The slowdown in UK business activity growth in February added to evidence that the economy has lost momentum after the impressive expansion seen at the end of last year, Markit said.
Input cost inflation increased to its highest level since August 2008, with Markit finding firms were struggled with rising costs associated with the weak pound, although optimism about the year ahead remained elevated by recent standards.
This led to the largest increase in prices charged by service providers for almost eight-and-a-half years. ■
What to read next
More inside POST