The approval allowed the first 710 to operate on the Overground West Anglia (London Liverpool St - Chingford/Cheshunt) services on March 3, with London deputy mayor for transport, Ms Heidi Alexander, joining passengers on one of the first services.

TfL ordered 45 four-car class 710 trains in June 2015 under a £260m contract, with delivery due in late 2018. The first trains entered service six months late in May 2019 on the newly-electrified Gospel Oak - Barking line.

The contract included options for a further 96 vehicles, including 31 four-car 25kV ac units for West Anglia services and 24 25kV ac/750V dc third-rail sets delivered as 18 four-car and six five-car sets for use on London Euston - Watford and North London Line Overground services. TfL has since exercised an option for 30 cars as six five-car trains.

The approval of the Aventra design for operation in multiple marks a major step forward for Bombardier, which will supply more than 1500 Aventra vehicles for multiple British operators this year.

Bombardier confirmed to IRJ that software development problems - in particular around multiple unit working - had delayed the introduction of the class 710/1 trains by over a year with more than 40 software versions tested before approval was obtained.

The software development for the Aventra and other European passenger trains is undertaken at several sites including in Britain, Sweden and India.

While the software on each Aventra train order is bespoke, the approval for multiple unit operation is a crucial step forward for the introduction of other Aventra orders which have been delayed, in particular the class 701 and class 720 trains for South Western Railway and Greater Anglia respectively.