The British Chambers of Commerce (BCC), which represents companies employing one in six UK workers, said the Bank of England's latest asset purchase programme may not be enough to avert a double-dip recession.
The business group estimated that the economy grew between 0.1 percent and 0.3 percent in the third quarter, and it warned that the downside risks were growing due to the euro zone debt crisis and worries about global demand.
"We can avoid a recession, but this relies on the government making some tough policy choices," said BCC Director General John Longworth. "The survey shows the real risks facing the economy and the need for the government to act now."
Separate estimates from an independent think tank were a bit more upbeat, suggesting the economy grew by 0.5 percent in the quarter through September.
However, the National Institute of Economic and Social Research (NIESR) said in its monthly estimate that the recovery from a deep recession that ended in 2009 was the weakest since World War One.
Britain's finance ministry said the NIESR report showed that the economy was continuing to grow, although the recovery would not be smooth.
"Other data published today similarly shows that the economy is recovering but that the financial turbulence in the euro zone and the weaker outlook for global growth will mean that the recovery will be choppy," it said in a statement.
Despite record low interest rates of 0.5 percent, Britain's economy has stagnated for nearly a year. Inflation of nearly 5 percent is squeezing people's living standards as wages rise slowly and unemployment has started to increase again.
"We're facing one of the toughest trading conditions this country has seen for decades," Phil Clarke, head of the country's biggest retailer Tesco said.
The government is cutting public spending to erase a budget deficit that peaked at nearly 11 percent of output and has little scope for tax cuts or extra spending to boost growth.
The Institute for Fiscal Studies said on Tuesday that the median income in Britain was expected to fall by 7 percent in real terms between 2010 and 2013, the largest three-year drop for 35 years.
That would push an extra 600,000 children and 800,000 adults into poverty, the think tank said in a report.
'Growing Sense of Gloom'
The Labour Party accuses the coalition of choking growth by doggedly sticking to its original austerity drive. There are question marks over how effective the central bank will be with its second round of quantitative easing to pump money into the economy.
"The latest numbers add to a growing sense of gloom about the health of the UK economy in the third quarter," said Chris Williamson, chief economist at Markit. "There is a substantial risk that the economy could fall back into contraction in the fourth quarter."
The results from the BCC survey of more than 6,000 companies mean the BCC is likely to revise down its growth forecasts for 2011 and 2012, the group's Chief Economist David Kern said.
"In September, my forecast was for 1.1 percent year-on-year (growth) for 2011. On the basis of what I know now, the figure would be 0.9 percent," Kern said.
Separate official figures showed British manufacturing output grew at its slowest pace for 18 months in the year to August, dampening government hopes that exports will help to kick start the faltering economy.
A big monthly rise in output from the volatile oil and gas sector lifted the broader industrial output measure, though it did little to change the overall downward trend.
There was also a surprise pick-up in retail sales in September, according to a survey by the British Retail Consortium (BRC). The trade body said like-for-like retail sales values were 0.3 percent higher compared to September 2010, beating forecasts for a 1 percent fall.
However, BRC Director General Stephen Robertson said that spending growth was below inflation, meaning customers are buying less than this time last year. "Underlying conditions remained weak," he added.
Economists said the official data and surveys pointed to a gloomy outlook, with consumer spending held back by squeezed household finances and exporters facing strong headwinds.
"All in all, it seems increasingly likely that the manufacturing and consumer sectors of the economy contracted in the third quarter," said Samuel Tombs, of Capital Economics.
"As a result, the risks of a renewed recession in the wider economy still appear to be growing."