The government says electricity firms will not be prosecuted over power cuts that hit parts of the UK last year.
Commuters using the Tube in south London and Kent were affected
Results from an official investigation into the cuts in London, Kent and the West Midlands have been sent in confidence to the companies involved.
Department of Trade and Industry lawyers have decided not to prosecute, but will be monitoring their response to recommendations in the report.
In August a power failure on the Tube caused chaos for thousands of people.
Commuters using the network and rail services in south London and Kent were affected and homes in the West Midlands were without power on 5 September.
Energy Minister Stephen Timms said recommendations from the Engineering Inspectorate were also sent so the firms could take the necessary action.
He said the companies could use the recommendations to "enhance the robustness" of their networks and make power cuts less likely in the future.
If the companies do not comply then the lawyers could take legal action.