Rail manufacturer Bombardier has struck a deal with Transport for London (TfL), which will see the firm provide another 57 cars for the city's overground network.

The carriages will be used to turn existing four-car trains into five-car services and the order is valued at approximately £88 million.

Delivery of the new Class 378 units will start in late 2014 and is expected to end in 2015.

Des McKeon, commercial director of Bombardier Transportation in the UK, said this contract underlines the strength of the relationship the firm has struck up with TfL.

"As well as delivering new, reliable trains we are improving availability and reliability together with the operator through our fleet maintenance offering," he remarked.

Bombardier - which recently announced revenues of $4.3 billion (£2.7 billion) for the first quarter of 2013 - has played a vital role in keeping London's public transport network rolling in recent years.

In 2012, the company worked around the clock to ensure 800 of its trains on nine key routes in the capital were able to cope with the increased demand brought about by the Olympic Games.