Senior lobbyists and politicians from Paris, France believe that 10,000 jobs in the financial sector could migrate to the city from London as a result of Brexit, with as many as 30,000 moving if jobs indirectly related to financial services are included in any count.

At a press conference in London on Monday, a panel of delegates from Paris — including the City's vice-mayor Jean-Louis Missika, the president of the Paris region, Valerie Pecresse, and Gerard Mestrallet, the chairman of the lobbyist Paris Europlace — addressed the future of the City of London and the movement of jobs to continental Europe after Brexit.

"Brexit is a long term process, so the moves will come slowly," Pecresse told reporters.

"Tens of thousands I would say," she added, saying that this number related to jobs directly in the financial services sector.

Pecresse's thoughts were further clarified by Paris Europlace CEO Arnaud de Bresson, who said: "The number of 10,000 is a good number," citing a survey undertaken by the lobby group.

"When we add the number of people who could be concerned in a different industry, then that gives something between 20,000 and 30,000 people, if we add indirect employees," de Bresson continued.

Both speakers were keen to add that these numbers are currently just estimates, with Pecresse saying: "It depends on the strategy of the firms and it will depend on how hard Brexit is."

Monday's conference was part of a concerted effort by Paris to position itself as the premier EU destination for banks looking to move staff out of Britain after Brexit.

Soon after Theresa May delivered a speech signalling that Britain will leave the Single Market, HSBC, JPMorgan, and UBS all warned about job relocations, and there are reports that Goldman Sachs is planning as much behind closed doors. Business Insider's Ben Moshinsky summed up the likely moves in January. They can be seen below:

There are two big areas of concern when it comes to London's role at the heart of European finance — financial passporting, and the clearing of euro-denominated trades in the City.

Current EU law allows European banks to operate branches in the UK that do not need to be separately capitalised from the parent company abroad. Similarly, non-EU banks, such as those from the US or Asia, can use their London subsidiary to sell services to clients across the EU. This has allowed London's financial centre to act as a hub for global firms looking to do business in the EU.

The use of this bank "passport," which allows banks in London to access the EU single market of 28 nations (including the UK), is now all but certain to disappear given that it is deeply tied to the single market.