British Prime Minister Theresa May has appointed Brexit supporter Stephen Barclay as "City minister" to oversee a financial services sector facing upheaval as Britain prepares to leave the European Union. 

Barclay's formal title is economic secretary to the treasury.

He is likely to be responsible for financial services policy and the government's relationship with firms such as banks, insurers and asset managers. 

Before he was elected to parliament in 2010, Barclay worked in financial regulation and then financial crime prevention at Barclays retail bank, according to his website. 

A lawyer by training, he supported leaving the EU at last year's referendum. 

Banks, trading platforms, insurers and asset managers in London are already making plans to open new bases in other parts of the EU, fearing a loss of access to the single market after March 2019 when Britain is due to leave the bloc. 

"His appointment comes at a time when the City's voice must be heard loud and clear," a City of London Corporation spokeswoman said. 

Barclay's experience in financial services will come as a relief after his predecessor, Simon Kirby, who lost his seat in last week's general election, dismayed the sector for having too little knowledge of finance at a critical time.

The return of a minority government in last week's election has raised hope in the financial sector for a "softer" Brexit, meaning some access to the EU market would be maintained.

As City minister, Kirby had been stripped of his remit in overseeing the impact of Brexit on Britain's large banking sector, a role handed to Lucy Neville-Rolfe, who quit this week. 

A finance ministry spokeswoman said the exact responsibilities of junior finance ministers had not been finalised.