Big British firms are deferring deals and hiring decisions ahead of a referendum on the country's European Union membership, adding to signs that uncertainty around the vote is weighing on the economy.
A survey of chief financial officers published by accountancy firm Deloitte shows chief financial officers are increasingly in favour of staying in the EU.
It shows 75 percent of the CFOs from FTSE 350 and other large private companies backed Britain's continued membership of the EU in the first three months of this year, up from 62 percent in the fourth quarter of 2015.
But the survey also showed 83 percent of CFOs thought the level of uncertainty facing their business was above normal, high or very high, a big jump from 64 percent at the end of 2015 and the highest level in more than three years.
The June 23 referendum represented the biggest single concern for businesses, ahead of slow growth in the euro zone.
"The referendum appears to already be contributing to a slowdown," David Sproul, chief executive of Deloitte, said.
"We have seen a marked slowdown in M&A activity as businesses put plans on hold for now."
Plans for hiring and capital spending had also decreased, Deloitte said.
Britain's economic growth slowed in late 2015, but remains stronger than in most other rich countries.
Economists say the approach of the referendum is likely to slow growth temporarily, but a vote to leave would deliver a bigger hit, at least in the short term.
The Deloitte survey found only 26 percent of firms had made contingency plans for a possible British exit of the EU, with 53 percent making no such plans and the rest declining to answer.