Business development forum London First has published its proposals for Crossrail 2.
The group, which is chaired by former Transport Secretary Lord Adonis, has set out recommendations for constructing a south-west to north-east line across London.
The line, which is based on the Chelsea-Hackney route, will provide additional capacity across central London at Euston, and Victoria, and it will support regeneration along the Lee Valley.
Initial estimates put the cost of Crossrail 2 at £12 billion.
London First said it had explored cheaper options, but found nothing that could deliver the same level of benefits.
Lord Adonis said: “The last 20 years has seen sustained investment and improvement in London’s transport infrastructure, which has been critical to London’s growth and prosperity. Bus, tube and rail services have all improved significantly.
“Crossrail is under construction, adding 10 per cent to London’s public transport capacity and enabling far more people to access jobs in central London. There is now a strong business-led consensus on the importance of sustained investment in London’s infrastructure, and its transport infrastructure in particular.
“So we need to begin detailed planning for the next generation of transport improvements now if London’s future growth is to be secured.”
A Chelsea-Hackney route has been safeguarded from development since 1991 but is due to be reviewed by the Department for Transport (DfT) this year.
“We urge the mayor and central government to take forward preparations for Crossrail 2, including a credible funding plan embracing the public and private sectors, with a view to construction in the 2020s,” added Lord Adonis.