Growth in the UK's services sector slumped to its slowest rate in three years in the run-up to the EU referendum, according to the closely watched survey.
The Markit/CIPS services purchasing managers' index (PMI) fell from 53.5 in May to 52.3 in June. Any figure above 50 indicates growth in the sector.
The majority of data was collected before the result of the EU referendum.
Markit said they survey also revealed the weakest expectations among businesses since December 2012.
The volume of new business received by UK service providers rose at a slightly faster rate in June, but the increase was still the second weakest seen since the upturn began three-and-a half years ago. Firms commonly reported that uncertainty linked to the EU referendum had often led to postponed or cancelled orders from customers.
The ongoing weakness of new business inflows led to a further decline in the level of outstanding work in the UK service sector in June. Backlogs declined for the third month running, dropping at the fastest rate since February 2013.
With the services sector accounting for around 80% of the UK's economy, Markit said June's figure suggests GDP grew just 0.2% in the second quarter.
Chris Williamson, chief economist at Markit, said: “A further slowing, and possible contraction, looks highly likely in coming months as a result of the uncertainty created by the EU referendum. However, with the June PMIs having already fallen into territory that would normally be associated with the Bank of England cutting interest rates, it’s unlikely that policymakers will wait for more data before unleashing additional monetary stimulus. More policy action is therefore likely in the coming weeks.”