The Enviro 400 was introduced in 2005 and has become a popular model among bus operators around the UK, as well as in Hong Kong. Initially available as a diesel, the model was adapted to a hybrid example known as the Enviro 400H. With a small change in body style introduced in 2009, Alexander Dennis Ltd relaunched the Enviro 400 in 2014 as the Enviro 400 MMC. A year later a third version was constructed, this being named the Enviro 400 City. This latter model being originally constructed for use in London, though sales in other towns and cities across the UK were received. The Enviro 400 has become a familiar sight on the streets of London.