Prime Minister Theresa May has urged banking chiefs to "emphasise the benefits" of preserving the UK's status as Europe's key financial centre when meeting with rival EU hubs.
It comes after Mrs May and Chancellor Philip Hammond hosted a roundtable of investment banks, insurers and infrastructure firms on Thursday to discuss the "opportunities and challenges" posed by Brexit.
Downing Street said the Prime Minister gave an overview of the UK's position in Brexit negotiations, including Britain's aim to agree to an implementation period by the end of March.
Goldman Sachs International chief executive Richard Gnodde, Aviva boss Mark Wilson and insurance market Lloyd's of London chief executive Inga Beale were among the City heavyweights who took part in the meeting, alongside Barclays chief executive Jes Staley and others from the likes of HSBC and Prudential, the Press Association understands.
"The business leaders were united in emphasising the need for as much certainty as possible," Downing Street said.
"The conclusion of phase one talks were deemed to have provided reassurance and the business leaders gave their views on how to maximise the benefits of an implementation period."
Mrs May also stressed the importance of extolling the UK's virtues when meeting with rival EU hubs.
"The Prime Minister asked that in their conversations in European capitals, the attendees emphasise the benefits for Europe as a whole of the UK's financial centre," Downing Street said.
City sources said that finance bosses were "encouraged" by the meeting, which was touted as one of the "most positive they'd been to in recent years".
Mrs May was understood to have shown a good understanding of the issues facing the financial services industry at the moment, including the importance of clinching the all-important transition deal.
But Conservative MP John Glen - who was handed the role of Economic Secretary to the Treasury and city minister this week as part of the Prime Minister's reshuffle - did not take part in the roundtable.
While his portfolio includes Brexit's impact on financial services, Mr Glen had already scheduled in a parliamentary debate on the role of banks in communities, which covered the recent spate of branch closures.
The meeting comes during a crunch time for UK-based financial services, as many foreign banks are expected to start moving key operations and staff to the EU in the coming months if negotiators fail to agree to a Brexit transition period that would allow financial services to conduct business across the bloc beyond 2019.
It would result in businesses fleeing to rival financial hubs including Dublin, Paris, Frankfurt and Luxembourg, where they can continue to benefit from passporting rights - though there are fears that thousands of jobs could leave the UK.
Among them is Lloyd's of London, which confirmed last year that it had chosen Brussels for its post-Brexit hub, in a move that is believed to involve moving about 100 jobs, while Barclays' Dublin office is set to serve as its EU hub in a move that could potentially double its local employee base by 150 staff.
Others like JP Morgan, which currently has 16,000 staff in the UK, will ramp up operations at a number of its EU sites with plans to move up to 1,000 London front and back office roles.
Goldman Sachs, which employs 6,500 UK staff, is taking a similar approach.
The Wall Street giant is set to at least double its Frankfurt office to 400 staff through a mix of relocations and local hires while Paris will serve as a dual hub.
Additional moves will be made to offices including Milan, Madrid, Stockholm and Dublin.