UPDATE 1-UK businesses slip into deepest downturn since 2016 in Nov -flash PMIs

* UK November flash composite PMI falls to 48.5 from 50.0

* Brexit and election uncertainty weighing on business morale

* IHS Markit says PMI data consistent with 0.2% q/q GDP fall

* Sterling drops to nine-day low against euro after data (Adds reaction from markets and economists)

LONDON, Nov 22 (Reuters) - British business suffered its deepest downturn since mid-2016 this month as the approach of a national election exacerbated uncertainty about Brexit, according to a survey which augured badly for the economy.

The first “flash” early reading of the IHS Markit/CIPS UK Purchasing Managers’ Indexes (PMI) for Britain showed on Friday that the decline in both the services and manufacturing sectors has quickened in November.

The readings suggested the world’s fifth-biggest economy is contracting at a quarterly pace of 0.2%, IHS Markit said, although the PMIs have overstated economic weakness recently, in part because of higher government spending ahead of Brexit.

Sterling fell to a nine-day low against the euro after the data and bond prices extended a rally that took 10-year yields down 5 basis points on the day.

Some economists said the survey weakness could be due to broader concerns about political uncertainty, rather than an outright fall in economic output.

“Markit’s survey has been excessively influenced by general concerns among businesses about the Brexit and political outlook and so has become a poor indicator of day-to-day economic activity,” Pantheon Macroeconomics’s Samuel Tombs said.

“Those concerns likely have only intensified since the general election campaign kicked off.”

The two main political parties contesting the Dec. 12 vote offer contrasting plans for the world’s fifth-largest economy.

Prime Minister Boris Johnson’s Conservatives promise to deliver Brexit, while Labour says it wants to be the most radical socialist government in British history.

Addressing a wilting British economy -- which has also been hit by the slowdown in the world economy caused by the U.S.-China trade war -- is likely to be among the first items in the next government’s in-tray.

“The PMI surveys are not only warning that the underlying trend in the economy is deteriorating markedly, but also that the labour market is cooling,” said Chris Williamson, chief business economist at survey compiler IHS Markit.

The PMI for the dominant services sector fell to 48.6 in November from 50.0 in October, its lowest level since July 2016, just after the Brexit vote.

Readings below 50 denote contraction.

The manufacturing PMI dropped to 48.3 from 49.6 as a stockpiling drive before the aborted Oct. 31 Brexit deadline evaporated.

The survey, closely watched at the Bank of England, adds weight to the views of two of its nine monetary policymakers who earlier this month voted for an interest rate cut.

The composite PMI, which combines the services business activity and services and manufacturing output readings, fell to 48.5 from 50.0, also its lowest level since July 2016.

In a bleak sign for coming months, backlogs of work declined at the fastest rate since 2012.

The final PMI readings for the manufacturing and services sectors will be published on Dec. 2 and Dec. 4 respectively.

Data show an average difference of 0.7 points in absolute terms between the “flash” and final versions of the UK composite PMI, compared with 0.2 points for the euro zone. (Additional reporting by David Milliken; Editing by Hugh Lawson and Catherine Evans)