There are very few sites in London where you can collect fossils, this is obviously because it is an urbanised area. It is more likely that temporary sites become available for the building and construction. The Eocene London Clay can be found beneath the City of London, so when new major construction projects begin, they extract from this layer. Abbey Wood is just about the only static location, but of which you need to join on a public event. The Eocene beds at Abbey Wood are dug out during field trips, often held once a year. The beds are full of shark, birds and mammals.