According to technology and investment advisory firm GP Bullhound: London remains home to Europe’s largest $1 billion tech company, but maintaining that lead post-Brexit may be more difficult.

Nowadays, London is home to 13 unicorn businesses, more than Madrid, Stockholm and Amsterdam combined. Emerging technology sector fintech the UK capital is one of the main sources of startups, with Monzo, TransferWise, and Revolut among the current unicorn crop in the city.

GP Bullhound’s data includes technology companies working in areas including artificial intelligence and machine learning, big data, cybersecurity, digital marketing and media, e-commerce, cloud computing, financial technology and healthcare technology.

He also predicts that UK hosts 25% of new $1 billion European companies made in the years to come. Taking into account their own figures say the UK now has 30% unicorns.

Sadiq Khan, Mayor of London, stressed that the British capital remains open to business, talent and investment from around the world. As reported by his communications agency: “London is an excellent place to start, grow and scale an international business. From artificial intelligence to fintech, London is home to many exciting companies that are leading the way in developing innovations and ideas to change the world. We love to welcome more international companies than any other city and today’s figures show that London is open to investment and talent from around the world.”

Manish Madhvani, Co-Founder and Managing Partner of GP Bullhound added: “London is the heart of Europe’s tech sceneand it’s great to see so many unicorns currently here, along with a few competitors that are likely to reach “next” status. The challenge now is to get the London unicorns on their feet, and above all for investors to support them with more resources so they can challenge the dominance of Silicon Valley, which earned Europe its first tech titan.

Few would argue that the UK, and London in particular, are Europe’s leading technology hubs. Will it maintain these gains after Brexit? In the past year, technology investment in the UK fell significantly, while investment in other European countries increased.

Four in ten tech companies say they are considering moving or setting up operations outside the UK as a result of Brexit.