One of the Government’s key transport projects – the upgrading and electrification of the main commuter rail lines into Dublin – is set to cost at least €600 million more than projected, new figures suggest.

The Dart expansion programme, which involves the provision of electrified rail services from Drogheda, Maynooth and Celbridge to Dublin city centre as well as upgraded signalling systems and junctions, was allocated €2 billion under the National Development Plan to run between 2018 and 2027.