Just seen this - also reported on BBC news.
Transport for London (TfL) has placed an £88 million order with Bombardier for 57 new Overground rail carriages.
The vehicles, which will be built in Derby, will increase all remaining Class 378 trains from four to five carriages on all but one Overground route the Gospel Oak to Barking line which will remain diesel powered.
Acting director for TfL London Rail, Jonathan Fox, said: With this order, the London Overground Capacity Improvement Programme is firmly underway to meet the demands of increasing numbers travelling on our network.
We are looking forward to introducing the longer trains from the end of 2014, starting on the East London Line.
In 2012/13, the network carried nearly 125 million passengers nearly four times the number carried when we launched in 2007. To enable this trend to continue and maintain our high levels for safe, reliable and frequent travel, we need to deliver more capacity by adding more carriages.
Des McKeon, commercial director UK, Bombardier Transportation, said: This contract underlines the strength of the long-standing relationship between Bombardier and Transport for London.
Bombardier is playing an important role helping TfL deliver increased capacity on the network. As well as delivering new, reliable trains we are improving availability and reliability together with the operator through our fleet maintenance offering.