Speculation that a decision on HS2 will be made early next week is mounting as the prime minister and key figures are understood to have held final talks on the controversial project.

The chancellor, Sajid Javid, who has publicly swung behind the scheme, and the transport secretary, Grant Shapps, are believed to have met Boris Johnson as the high-speed line continues to divide opinion among backbenchers.

Shapps told the Commons on Thursday that a decision was due “next month”, though the expectation is that it will be made public early next week while avoiding a clash with Johnson’s major speech on a future trade deal with the EU.

Shapps told MPs during transport questions in the Commons on Thursday that they “won’t have to wait very long” for a final announcement.

The Conservative mayor of the West Midlands, Andy Street, who has been a strong advocate for the line and its potential to help the region’s economy, told the Guardian: “All of my instinct is the argument will be won.”

Javid is understood to “broadly back” the project, which has already prompted deep divisions within the Conservative party. Its cost has been estimated at up to £106bn, nearly doubling from a figure of £56bn in 2015.

But opposition to the high-speed line – which will link London, Birmingham, the east Midlands, Manchester and Leeds – remains strong, with critics raising concerns over rising costs and environmental impact.

The newly elected Conservative MP Greg Smith, who represents Buckingham, a constituency where some people have been forced out of their homes to make way for HS2, indicated he would rebel against the government in any Commons vote on the project.

Asked whether he was willing to defeat his own government, he told BBC Radio 4’s Today programme: “I was very clear in the general election campaign that I am opposed to HS2. It is absolutely wrong for my constituency and I believe it to be wrong for the country as well, and I made very clear commitments in the general election that, come what may, I will oppose HS2.

Q&A How much work has already been done on HS2 - and how much has it cost? Show As of March 2019, £7.4bn had been spent. Much of the work done so far has been on paper: detailed engineering designs of the length of the route, years of public consultation, and legislation. Officially launched by Labour in 2009, HS2 was reviewed and tweaked by the coalition government and green-lighted in 2012. So far money has been spent on detailed engineering designs of the length of the route, years of public consultation, and legislation. Buying land along the route, either for direct demolition or to relieve blighted homeowners, has accounted for a large total of the £7.4bn invested to date. In terms of physical activity, so-called preparatory works have started, although no track or tunnel has yet been built. At the southern end, HS2 has demolished housing estates, parks and office blocks around Euston, and started moving tens of thousands of skeletons out of the way. Train depots and industrial estates have been razed to build another HS2 station at Old Oak Common, while brownfield sites in Birmingham have been levelled for the Curzon Street station and approach. According to HS2, work has taken place at 250 sites, including archaeological digs and tree planting as well as construction. Gwyn Topham Transport correspondent

“What I really want to get on with, though, is convincing the government that there are better projects that we can deliver, which will improve people’s lives.”

The rising budget could become a stumbling block as Javid has ordered ministers, in a letter co-signed by Johnson, to identify 5% cuts in their departments so the government is free to plough funds into manifesto pledges on improving the NHS, education and policing.

Smith said his constituents were “extremely angry” about the project, adding: “HS2 rips through the middle of Buckinghamshire as a whole, not just my constituency, and we have many people who are already turfed out of their homes, having, incidentally, not been paid for those homes, farms cut in two, villages decimated.

“But I think this case is twofold. One is the environmental destruction, which is outrageous, especially in Buckinghamshire where there is no benefit whatsoever for local people, no stop, no ability to use this line.

“But bigger than that is the unaffordability of HS2. Lord Berkeley’s review [into HS2] found that for every pound spent, we’re only going to get 60p back.” The review, overseen by the former HS2 chair Doug Oakervee, was leaked in November but Berkeley demanded that his name be removed after the leak suggested that the line should be built in full.

Timeline HS2 - over-budget and behind schedule Show High Speed Two Ltd is set up by the Labour government to examine possibilities for increasing high-speed rail capacity in the UK. The project is split into two phases - London to Birmingham forms phase one, with phase two extending the route to Manchester and Leeds. The transport secretary, Conservative Justine Greening, announces the decision to build HS2. A judicial review is called into the HS2 decision. Lord Justice Ouseley upholds one of the 10 grounds for complaint about HS2 in the judicial review – the claim that the government had acted unfairly and unlawfully when consulting on compensation for homeowners affected by the route. The Conservative prime minister, David Cameron, describes the project as "absolutely vital" as MPs approve funding. The high-speed rail (London-West Midlands) bill is formally introduced in parliament. After freedom of information requests, a 2012 Department for Transport viability report into HS2 is released, revealing the department considered it unaffordable. Allan Cook replaces Sir Terry Morgan as chair of HS2, after the latter fails to deliver the opening of the Crossrail project in London on schedule. A report from the New Economics Foundation suggests HS2 will deliver the most benefit to London, and exacerbate regional inequality. A fresh government review begins into HS2 into whether the scheme should be approved, amended or scrapped entirely. The Conservative transport secretary, Grant Shapps, announces that full HS2 services between London and Birmingham will be delayed by up to five years to 2031, and that the final completion of the northern section of the high-speed rail network would likely be delayed by seven years until 2040. He also confirmed the budget had escalated from the official £56bn at 2015 prices to up to £88bn at today’s prices. After a period of review, prime minister Boris Johnson announces that HS2 will go ahead, alongside a package of measures aimed at improving bus and cycling links outside of London.

However, Street said the cost of the project would be paid over many decades and the economic case made in the Oakervee review, which is yet to be released, showed there is a strong economic case for the project.

He said: “It was very significant the chancellor put his weight behind it. The chancellor said he pored over the numbers and I know as a member of the Oakervee panel that all the costs were there and the likely benefits, and there was a value for money answer.

“You’ll be paying it back over 50 to 100 years, just as the people who built the Victorian railways or indeed the people who built the Channel tunnel would think in that timeframe. On these really big projects that’s how you’ve got to think about it.”

Politically he said it would be unthinkable to reject the scheme now.

“We just had the breaching of the red wall and this is to invest in those places that turned to the Conservatives,” he said.

Whitehall’s spending watchdog, the National Audit Office, warned earlier this month that HS2 was over budget and behind schedule because the risks and complexity of the project had been underestimated. The final cost was impossible to estimate “with certainty”, the watchdog said.

Phase one, running between London and Birmingham, was to open in 2026 but services are now expected to launch between 2031 and 2036.