* City's output to increase by 16 bln pounds by 2025 -study
* 39,000 City jobs would be created in next 10 years -study
* EU membership incredibly important for City -lawmaker
* City growth would help generate 145,000 new jobs in London
By Matt Scuffham
LONDON, June 3 (Reuters) - London's financial district willgrow its economic output by more than a third and employ 10percent more people over the next decade if threats including apossible British exit from the European Union don't materialise,according to a study.
A report commissioned by the City of London Corporation,which promotes London as a financial centre, said the Citygenerated 45 billion pounds ($69 billion) in what it termedeconomic output in 2014, with that figure expected to grow by 16billion in the next 10 years.
That growth will help create 39,000 new jobs in the City -- as the financial district is known -- and where 397,000 workerswere employed last year. Ninety percent of the output gains and70 percent of employment growth would be within finance &insurance, media, IT & communications, and legal & accountingbusinesses, the study said.
Growth within the City will help contribute to the creationof 145,000 new jobs across London as a whole, it said.
"This report shows how vital the City's success is to growthin London and the UK," said Mark Boleat, Chairman of Policy &Resources at the City of London Corporation.
The study said the possibility of 'Brexit', a lack ofskilled employees, unaffordable housing, and limits on aviationcapacity could all pose a threat to achieving this level ofgrowth.
Prime Minister David Cameron has pledged to renegotiateBritain's ties with Europe and then give voters a referendum onEU membership by the end of 2017.
Conservative Mark Garnier, who served on parliament'sTreasury Select Committee, said on Tuesday that Britain'scontinued membership of the EU was "incredibly important" forthe country's financial services industry.
"The UK and the City of London is not a destination in itsown right, it's a gateway to the single market in Europe. It'simportant we maintain our position in Europe and become aninfluential member," he told an industry conference.
The "Brexit" risk is also causing major politicaluncertainty for the insurance industry, the chief executive ofthe Association of British Insurers said on Tuesday.
The forecast for job growth in the City of London comes wheninvestment banks across Europe are slashing thousands of jobs asthey restructure to meet tougher demands from regulators,pulling out from businesses which are no longer seen asproviding adequate returns. ($1 = 0.6527 pounds) (Additional reporting by Jamie McGeever and Huw Jones; Editingby Keith Weir)
HSBC Holdings (HSBA)