Greater Anglia is preparing to introduce all its new trains into service by the summer of 2022 - which is likely to herald the departure of the existing fleet of electric suburban units.

The first of the new Bombardier Aventra trains have now entered service in south Essex on lines from Liverpool Street to Southend and Braintree. They have travelled to Colchester and Ipswich on crew-training trips but have not yet carried passengers to these parts of the network.

However, they are expected to enter revenue-earning service on these routes - along with the lines to Harwich and Clacton - in the spring alongside existing trains.

Originally they were planned to be a mixture of five and ten-carriage trains. But the order was changed last year so all the trains will now be five-cars long although two can be coupled together to make a longer train.

During the summer the new trains will be operating alongside existing suburban trains on routes from London to Essex and as far as Ipswich. A few services with the Aventras could run through to Norwich.

Early next year the new trains are expected to be introduced on West Anglia services from Liverpool Street to Cambridge.

East Anglian Daily Times: There are 10 Intercity trains, on the left, and 10 Stansted Expresses now in service with Greater Anglia.There are 10 Intercity trains, on the left, and 10 Stansted Expresses now in service with Greater Anglia. (Image: Archant)

Eventually there will be 133 five-carriage suburban trains operating alongside the 10 InterCity trains, 10 Stansted Express trains and 38 bimode diesel/electric trains used on regional services across East Anglia.

East Anglian Daily Times: A Stadler bimode train at Felixstowe station.A Stadler bimode train at Felixstowe station. (Image: Archant)

When the last Aventras enter service in the middle of 2022, almost all the passenger trains in service in East Anglia will less than four years old - something that hasn't happened since the 1850s!

One aspect of the new trains' operation that has not been set in stone yet is where all of them will be maintained and serviced.

Greater Anglia's main service centre for them will the Ilford depot in east London - but other centres will also be used to ensure they are in top condition before going into service.

A new depot has been planned for Parkeston on the outskirts of Harwich - but there is no firm date for work to start on that and the company could not say whether it would be going ahead with it.