At the same time, the UK's leading banks have called for a special three year deal protecting the freedom of movement for financial services workers post-Brexit, according to a report in the Financial Times.

The worry about a tech skills gap was reported in a survey of 5,400 tech founders by industry body Tech London Advocates which revealed that more than a third had failed to complete prospective hires because of worries about immigration.

The report comes a day after the UK government announced a plan to double the amount of tier 1 work visas granted to "exceptional talent"  to 2,000 a year specifically to quell any fears over a so-called Brexodus of highly skilled tech workers from Europe working in the UK or a failure to recruit any more in the future.

Announcing the measures, British prime minister Teresa May said she was in no doubt that the UK "would remain a brilliant place to build a tech business" post-Brexit.

But  some of the tech leaders invited to Downing Street to hear the plan told the Financial Times that the measures, while welcome, would not be enough and called for the visa plans to be extended, not least in the provision of tier 2 work visas for mid-ranking web and software engineers that are currently in short supply.

And Tech London Advocates founder Russ Shaw told the Financial Times that many startups also require administrative assistance when dealing with work visas and called for the rules around the recruitment of foreign nationals to be relaxed so that venture capital firms or tech incubators could sponsor some of the visa applications and thereby relief the pressure on both startups and the Home Office.

It is not just tech firms that are concerned about the personnel effects of Brexit. Numerous banks have warned about losing key staff as a result of post-Brexit immigration issues.

A report just published by industry banking body UK Finance, consultant Global Counsel and law firm Clifford Chance has called on the government to enshrine freedom of movement for financial services workers across Europe and the UK for at least three years following Brexit as part of a UK-EU free trade agreement that is “based on mutual acceptance of regulatory and supervisory co-operation and reciprocity”,

Britan's Brexit minsiter David Davis had referred to plans to negotiate a deal for the UK's financial services sector earlier this week and while UK Finance chief executive Stephen Jones told the Financial Times that the minister had been "constructive", he also called for more urgency saying that "we are wasting time and need to start negotiating this now".