Boris Johnson, the mayor of London has been in New York extolling the virtues of London as a hub for tech and digital start-ups and he is not wrong. In 2014 some 1.4 billion dollars of investment was made in digital businesses in London with some 250,000 people employed in the sector. What are the advantages of London over say San Francisco? The staff and legal costs of setting up a business are lower. There is an existing body of expertise willing and ready to make things work. The weakness is funding. London cannot compare with 70 to 160 billion dollar investment made in Silicon Valley by venture companies. Nevertheless, London remains a favoured destination for tech and digital investment.