British manufacturers reported the fastest fall in export demand this month since December 2020, just before Britain left the European Union's single market, the Confederation of British Industry said on Monday.

The CBI's monthly industrial trends survey showed that the export order balance sank to -44 in September from -22 in August. The overall order book fell to a 10-month low of -35 from -22, in contrast to economists' expectations in a Reuters poll for it to hold broadly steady.

"This was a uniformly disappointing set of results for the manufacturing sector, with output falling over the past quarter, order books deteriorating and manufacturers expecting activity to soften further in the remaining months of the year," CBI economist Ben Jones said.

The weak export figures chime with a continued slide in euro zone manufacturing activity in September purchasing managers' index data published earlier on Monday - although the UK manufacturing PMI continued to show expanding activity.

The CBI data showed a sharp fall in factory output for the third quarter, and expectations for a further smaller decline in the final quarter of this year.

(Reporting by David Milliken)