The National Audit Office (NAO) has said it expects to publish an update to its 2013 report into the Thameslink upgrade this autumn.
Sponsored by the Department for Transport (DfT), the £7bn project involves track and signalling upgrades to the Thameslink route running north to south through central London, to increase capacity by 50% on the line. Its completion date was pushed back to 2018, having originally been due to finish in 2015.
The update will examine how the DfT has dealt with cost and scheduling pressures since the NAO last published an update on Thameslink upgrade progress in 2013.
At the time the NAO had warned that although the initial phase of the project had been completed on time and to budget in 2011, the second phase of the project may not be completed by the revised 2018 date.
It also expressed concern that delays could mean infrastructure built on the programme would not be compatible with new trains. Network Rail said it had a testing programme designed so it could learn as much as possible about the equipment before using it on the railway.
The Thameslink Programme also includes the rebuild of London Bridge station, which is two-thirds complete.
The DfT and Network Rail have been contacted for comment. Evidence to the study can be submitted at firstname.lastname@example.org.