The tests are focused on exploring the reactions of pedestrians, drivers and other road users to the cars.
Transport Minister Claire Perry said: "Driverless cars are the future. I want the UK to be open-minded and embrace a technology that could transform our roads and open up a brand-new route for global investment.
"The breadth of public and private sector involvement in the GATEway Project is testament to the potential of driverless cars and how much we stand to gain from testing them further."
Greenwich, Milton Keynes and Coventry are the three areas in which the trials are taking place.
In Greenwich the Meridian Shuttle, took its first journey on Wednesday.
In total, eight cars are set to run with passengers in the south-east London area this summer.
Royal Borough of Greenwich's cabinet member, Councillor Sizwe James, shown above trying out the driverless car outside The O2, said: "The technology sector is really important for us here in Greenwich and we know that a project like this - with global interest - will bring new jobs to the area.
"New companies involved in this and other so-called Smart City technology are already moving their business to Greenwich and we know more will follow. We already have more than 1,000 technology businesses based in the Royal Borough of Greenwich and as this sector grows it will help to further strengthen the local economy."