The fintech community has, like most other business sectors, come out broadly against brexit. A recent Financial News poll of financial technology firms found that more than two-thirds believe leaving the EU would be detrimental to the UK startup scene.

Last week US payment systems giant ACI Worldwide entered the debate, warning that a Brexit would be "disastrous" for the UK fintech community and seriously jeopardise London's role as a central hub for financial services in Europe.

Now, in a report commissioned by Fintech Week, William Garrity Associates has tried to calculate the cost of a leave vote, estimating that billions of pounds are at stake because of 10 factors which make Brexit bad for UK fintech.

Among them are the human capital costs which will arise from the end of free movement of EU nationals; reduced access to EU markets, the loss of the UK's leadership in 'regtech'; and a lack of say in the formulation of the single European capital market and digital single market initiatives.

Ian Dowson, CEO, William Garrity Associates, says: "When I started to analyse the implications of Brexit on UK companies in the fintech space I tried exceptionally hard to find positives on each of the 10 criteria. I failed. Brexit will be catastrophic for UK fintech companies.

"The alternatives of integrating closer with the USA or negotiating a new deal with the EU will take an extraordinary amount of time and effort, at least five years’ worth and in the life of a start-up or innovator, this is a lifetime. Any sensible company looking to scale will have no choice but to relocate to the EU; I would if I was in their position."

Among the names coming out in favour of Remain, is Sean Park, founder of venture investment and advisory firm Anthemis, who warns: "The negative impact on the two most crucial success factors for the fintech start-ups, namely access to markets in other EU countries and access to talent from these countries would be huge if Britain choses to call time on its relationship with Europe, not to mention access to funding from EU based VCs.

"The UK, especially London, which at the moment is the world’s highest earning fintech sector, stands a very real risk of losing some of its most promising home-grown start-ups to other global hubs that would inevitably overtake it."

Meanwhile, a straw poll of start-ups at Barclays’ Rise accelerator in the east of London shows concerns among the country’s new breed of entrepreneurs, ranging from access to talent, to pricing and the viability of their business model should the country decide to leave the economic bloc.

Another voice warning against Brexit is Simon Black, CEO of Ppro Group, who warns of the potential impact on cross-border e-commerce: "Research reveals that by 2020 some 40.6% of all British e-commerce revenue will come from sales outside of its borders. Europe itself is expected to account for £16.7 billion of all e-commerce revenue for British businesses by the end of the decade.

"If the Brexit was to go ahead, the viability of continuing our leadership in cross border e-commerce would be under severe threat, impacting the very livelihoods of digitally-minded British businesses."

Hiroki Takeuchi, CEO of GoCardless, which processes $2billion payments for 20,000 businesses across Europe, believes damage has already been done by Brexit, regardless of the outcome:

“Whichever way the vote goes, we are already starting to see the impact of the referendum on UK startups. Potential US customers are holding off on signing contracts and their perception of London as a steady, stable staging post for the rest of Europe is coming into question.

“Early on in our company’s life, we were one of very few companies that chose to move back to the UK after Y Combinator, a US incubator programme. One of the key attractions in doing this was London’s political and geographical strength within the EU. If we had to make the same decision in a post-Brexit world, it’s hard to say we would make the same choice.”

Not everyone thinks that Brexit would be bad for fintech. Former minister of state for trade and investment Digby Jones recently wrote in City AM that the fintech boom means that leaving the EU won't hurt exports.

"The UK is in an exciting position at the epicentre of the fintech boom, and I believe financial technology solutions will act as a one-stop shop for international trade, securing payments and removing the need for letters of credit, currency hedging, insurance, legal advice and bank-led funding in one step," says Jones.

Meanwhile, Chris Gledhill of challenger bank Secco has used Finextra's pages to argue that the EU is a bureaucratic relic of the past, concluding: "The EU is a burning platform and it's time the UK got off - for the sake of UK FinTech and the UK in general I believe now is the right time to leave the EU."

Reflecting the unceratinty surrounding the vote, UK fintech unicorn TransferWise has announced plans to suspend GBP transaction on Thusday, citing FX volatility issues.