I think there are various factors to why that constituency has the highest amount of bus users in the country. Rail services are on the fringe of the area and compared to somewhere like Forest Hill have less regular services. It's viable to use the bus as an alternative to the train to central London. As Jeremy mentions, it's still a deprived part of London. The buses connect to Oval, Vauxhall and Elephant & Castle tube stations. In the case of the Elephant, it can work out cheaper to travel to the Elephant or Vauxhall on the bus and pay ?2.20 single on the tube for a Zone 1 journey in the morning peak. Anyone who has travelled on a bus along the Walworth Road or Camberwell New Road can say the buses are always packed.