How a 90-second power outage sparked chaos for rail commuters

The power failure which hit a Network Rail operations centre in Manchester was a rare incident.

But after commuters were left facing chaos , it has raised questions about how a short outage at one operating centre could have a widespread impact.

Network Rail will face scrutiny for how its systems coped and responded to the outage.

That's the publicly-owned body whose job it is to operate and maintain Britain's railway infrastructure. That means the tracks, signals, embankments and major stations.

It was at Network Rail's operating centre in Manchester that the problem started. Its operating centres are where crucial controls are housed that let trains run safely across the country, with Manchester's centre responsible for large parts of the North West.

It was hit by a power cut in the area, which was resolved within 90 seconds. And despite having a backup supply, given the centre's importance, this failed to kick in as quickly as expected.

Because signalling was affected - think of that as the traffic lights of the railway - trains had to stop.

Systems had to be rebooted. But there was some damage to the systems controlling signalling, and that took time to fix because of the need to replace certain parts.