Transport for London (TfL) has secured a £1bn loan from the European Investment Bank (EIB) for the ongoing £16bn Crossrail project.
The loan is part of TfL's commitment to raise £2.4bn for the project of the total £7.7bn it will jointly raise with the Greater London Authority.
London Mayor Boris Johnson said this is one of the largest loans ever secured for a transport project.
EIB's vice-president Simon Brooks said the project will help develop London as a sustainable world city by reducing congestion and pollution for the benefit of Londoners, commuters and visitors.
"It will also link London more efficiently into the European and global transport networks," Brooks said.
The project, scheduled to finish in 2017, will see a 72-mile rail route starting from Maidenhead in Berkshire to Heathrow airport via central London to Shenfield in Essex.