Clusters such as Silicon Valley are liked by policymakers for many reasons. They are visible, often prestigious, and are effectively cities in miniature. They take the things that make urban economies work and amplify and concentrate them in a particular place.

London's Tech City programme was launched in 2010 to accelerate its tech cluster in Shoreditch and, by 2014, the then Mayor of London Boris Johnson was hailing it a huge success.

But did the policy have any effect? And how might you approach evaluation when there are no like-for-like comparators?

For this episode of City Talks, Dr Max Nathan joins Andrew Carter to discuss his recent paper 'Does light touch cluster policy work? Evaluating the Tech City programme'.