The flow of financial services between the European Union and Britain will be less fluid from January whatever happens in talks on a future free trade deal, the EU's financial services chief designate has said.

Britain left the EU last January and unfettered access to the single market under transition arrangements ends on 31 December.

Brussels and London are in talks on a free trade agreement, though financial services are being handled separately.

"Under all circumstances, deal or no deal, trading in financial services will be different and less fluid as of the first of January next year," Mairead McGuinness told the European Parliament.

If confirmed by the parliament, Ms McGuinness will lead the European Commission's work that will decide how much EU access the City of London will have from January.

"We need to avoid being overly dependent on a third country for key financial services," she said in a confirmation hearing on her appointment as financial services commissioner.

A veteran member of the European Parliament and former journalist, Ms McGuinness said it took investigative journalism to uncover the €1.9 billion hole in the balance sheet of now collapsed German payments company Wirecard.

"The Wirecard scandal is a shocking tale of fraud and failure of supervision," Ms McGuinness said.

"We need to take a long hard look at what went wrong there and learn the lesson… It's such an enormous issue."

EU states have pushed back in the past on more common supervision in markets, fearful of losing more regulatory sovereignty. The Wirecard collapse has prompted the European Commission to revisit the question.