(Adds more detail, quotes and context)
LONDON, Aug 4 (Reuters) - British new car registrations fell for a fourth consecutive month in July, the longest run of declines since 2011, in the latest sign of how uncertainty about Brexit is hitting Britain's economy, a car lobby group said on Friday.
Demand fell across business, fleet and private sales with total registrations down by 9.3 percent compared with July last year, the Society of Motor Manufacturers and Traders (SMMT) said.
In the first seven months of the year as a whole, private sales were down 5 percent, with business registrations down 0.2 percent and fleet sales up slightly at 0.1 percent, leaving total registrations down 2.2 percent.
"The fall in consumer and business confidence is having a knock-on effect on demand in the new car market and government must act quickly to provide concrete plans regarding Brexit," said SMMT Chief Executive Mike Hawes.
Bank of England Governor Mark Carney said on Thursday uncertainty around Britain's split with the European Union was weighing on the economy.
Samuel Tombs, an economist with Pantheon Macroeconomics, warned that "the downturn has further to run."
The hit to consumer sentiment from June's national election - in which Prime Minister Theresa May lost her parliamentary majority - could push registrations down further as sales tend to lag six months behind consumer confidence, he said.
Registrations for alternatively fueled vehicles, however, soared 64.9 percent, the SMMT said.
The government said on July 26 that sales of petrol and diesel cars would be banned from 2040. (Reporting by Emma Rumney; Editing by William Schomberg and Gareth Jones)