Google is supporting a pressure group that says the UK is being held back by a lack of immigration visas for tech workers

The UK's fastest-growing startups need to be given special immigration visas if they are to have any chance of growing to the size of Google or Facebook, according to the Scale-Up Institute.

The Institute, founded by investor Sherry Coutu and LinkedIn cofounder Reid Hoffman, argues that a dearth of talented technologists in the UK and Europe is holding back startups with great potential.

Coutu's organisation, which is backed by Google and the London Stock Exchange, believes that UK startups would have more chance of becoming global giants if they were able to hire talented programmers from wherever they happen to be in the world.

At the moment this isn't always possible due to immigration laws which prevent companies from hiring individuals outside Europe. The number of visas for foreign tech workers hit its maximum cap in June - leaving companies unable to recruit further.

Speaking on a panel at the sixth Tech London Advocates conference, Irene Graham, the incoming CEO at the Start-Up Institute, said: "We really want to see a scale-up visa coming in to help [fast-growing] companies get that quick access to talent.

"You're building and growing fast, and it's taking months and months and months to get that skill set in. We need that to happen faster. That's the purpose of the scale-up visa."

Business Insider also asked the Scale-Up Institute how close a Scale-Up visa is to becoming reality and is awaiting a response.

According to London & Partners, the city's promotional agency, there are 71,000 software developers in the capital, But Silicon Valley is the place that creates more unicorns than any other. It's easier for US companies to get visas for foreign tech workers - the H1-B visa programme last year brought 162,000 tech workers into the US.

The UK government currently gives out only 20,700 visas to skilled non-EU professionals annually. But that cap was hit in June, making it impossible for companies like Google UK and Facebook UK to hire people outside Europe during the rest of the year.

The UK is home to 17 of the 40 European tech companies that have achieved $1 billion valuations in the last year. Examples include TransferWise, Shazam, and JustEat, according to GP Bullhound. But the Scale-Up Institute believes that the UK now needs to focus on creating companies worth $100 billion.

The Institute was launched after Coutu published the Scale-Up Report in 2014. In the report, Coutu argues that the government should focus its efforts on supporting ambitious businesses in scaling to their full potential, providing six recommendations including closing the skills gap, improved access to finance and developing "scale-up leadership."

Government quango Tech City UK is also able to give out 200 visas to exceptionally talented technologists outside the EU but last year a freedom of information request showed that it gave out just seven of them.