National Grid has announced that tunnelling work on the 32km of tunnels on the London Power Tunnel project has been completed.
The new tunnel network has been developed to enable new high voltage electricity cables to be laid in order to meet future energy needs in London.
Tunnel boring machines (TBMs) for the scheme were launched by Skanska and Costain four years ago and work is already underway to install electricity cables in some sections of the network.
The final TBM breakthrough took place at Kensal Green.
The depths of the tunnels vary from 20m to 60m below ground and were excavated mainly within London Clay. Spoil from the tunnels has been used to carry out remediation at a number of former gasworks sites owned by National Grid in London.
Cables are already being laid in some of the first sections of tunnels and are expected to be powered up later this year. The complete network is expected to be operational by 2017.