New trains planned to revolutionise suburban travel in Essex and on the line to Ipswich could be delayed – forcing Greater Anglia to continue using older electric units on the routes.

The Bombardier Aventra trains being built at Derby are due to start arriving in East Anglia in the autumn and should start taking over suburban services at the end of the year.

However similar trains that have been delivered to London Overground from 2017 have still not entered passenger service because testing on the tracks around the capital have thrown up unexpected issues.

London Overground and Bombardier say they hope they will enter service during the first half of this year, but there is no fixed date.

Greater Anglia bosses are watching what is happening with interest – their trains will also have to be tested before entering service.

A spokesman said: “At the moment we are not facing any delays but we are watching the situation and are in regular contact with Bombardier.”

All Greater Anglia’s suburban trains, from London to Essex, Ipswich, and Cambridge, are due to be operated by Aventras by the end of 2020.

The trains are currently being built at the Derby factory – a total of 111 trains with a total of 665 carriages – alongside the London Overground orders.

There are no testing problems with the Swiss-built Stadler units which will be used on the InterCity trains from Ipswich and Norwich to London and on rural and cross-country services.

The first bimode electric/diesel units for rural services have been on test in the region since the end of last year and Greater Anglia managing director Jamie Burles told the Great Eastern Main Line rail conference they had passed all these tests “with flying colours.”

Last week they started testing runs in Suffolk and Essex after weeks of testing in Norfolk.

They are expected to start appearing in service in the middle of the year and to have taken over all rural routes by the start of 2020.

The first InterCity trains are expected to arrive in the spring and are expected to enter service in the summer. Greater Anglia hopes the existing 40-year-old carriages will all be phased out early next year by which time they will not meet new safety standards governing door locking.