Plans for a £20bn railway running between north-east and south-west London will be handed a boost with a slug of funding from the Treasury in next week’s Budget.

It is understood that the Chancellor, George Osborne, is preparing to give more than £100m to develop the Crossrail 2 proposal. This includes working out the finer details of the route, technical assessments and identifying potential planning issues, before a decade-long construction programme starts in 2020.

Consultations in 2013 and last year found that the public is overwhelmingly in favour of both the core metropolitan project, running from Tottenham Hale down to Wimbledon, as well as Transport for London’s preferred option of Crossrail 2 becoming a regional line that stretches into Hertfordshire and Surrey.

WS Atkins, Mott Macdonald, Vinci Construction, Aecom, and CH2M Hill are among the big-name consultants and engineers already drawing up plans for Crossrail 2.

A source close to Crossrail said: “There is likely to be some seed-corn money in the Budget and it will not be an insignificant number, probably north of £100m, just to keep the project moving. The consultation is done; this will help get it through to planning.”

Transport for London was quietly handed a business case by infrastructure experts recently showing that Crossrail 2 will be of huge economic benefit to the capital and neighbouring counties. A source who has seen that report said: “There’s significant benefit in terms of this project helping [transport] with the future growth of London.”

A third source said Crossrail 2 will also help the argument for the £42.6bn High Speed Two scheme, which will get commuters from London to Birmingham in 49 minutes but is facing fierce criticism from environmental campaigners as it goes through the parliamentary approval process. Crossrail 2 will run through Euston station, where HS2 starts, greatly improving the connections to other parts of London for those commuting to the capital.

The first Crossrail, which runs from Reading and Heathrow in the west to Shenfield and Abbey Wood in the east via 48km of new tunnels under London, has been considered a model construction project.

The first trains are due to run by late 2018, increasing the capital’s rail capacity by 10 per cent and bringing an extra 1.5 million people within 45 minutes of central London.