Boris Johnson is expected to confirm HS2 will go ahead on Tuesday, despite concerns over its budget and the environmental impact of construction.
The controversial high-speed railway scheme is likely to be discussed at a Cabinet meeting in the morning, before the Prime Minister makes a statement on the project.
It has been reported that Mr Johnson will give the green light for Phase 1 between London and Birmingham, but say more analysis is needed on the cost of the route extending further north to Manchester and Leeds.
High-speed trains will also run beyond the new lines on existing tracks as far as Edinburgh and Glasgow.
HS2 Ltd - the Government-owned company responsible for developing and building the railway - says it will boost capacity and cut journey times.
- ITV News Political Correspondent Romilly Weeks on the balancing act the PM has had to perform over HS2
Former HS2 Ltd chairman Douglas Oakervee was commissioned by the Government in August 2019 to lead a review into whether or not the programme should be scrapped amid rising costs and delays.
It has been widely leaked that the review found HS2 could cost up to £106 billion, but concluded that "on balance" it should continue.
HS2's original budget was £32.7 billion at 2011 prices.
It was due to open in December 2026, but HS2 Ltd chairman Allan Cook said last year it would be "prudent to plan for an opening between 2028 and 2031".
Last month, Whitehall's spending watchdog said the scheme is over budget and behind schedule because its complexity and risks were under-estimated.
The National Audit Office warned that it is impossible to "estimate with certainty" what the final cost could be.
HS2 has been the subject of years of intensive lobbying from politicians and opposition groups.
Several environmental organisations claim building it will cause huge damage to natural habitats, including dozens of ancient woodlands.
Communities living on or near the route have expressed anger at the impact on their lives, while many people have said the project is simply too expensive and the money would be better spent elsewhere.
For Labour, shadow transport secretary Andy McDonald said the measures would not reverse the damage done by years of Conservative cuts.
"After years of under-investment and cuts, this unambitious announcement is nowhere near enough to make the difference that transport users, our economy or our environment need," he said.
"The Conservatives are refusing to reverse their colossal £645 million-a-year cuts to bus budgets, which have caused thousands of routes to be axed and fares to soar."
The announcement will come alongside a move to invest £5 billion in order to overhaul bus and cycle links in English regions outside of London.
Mr Johnson will say the five-year funding package will provide more frequent services and simpler, more affordable fares.
It will also allow for new priority bus routes and the purchase of at least 4,000 zero-emission buses in England and Wales.
The move will be seen as a sop to placate Tory MPs critical of HS2 who have argued the money would be better spent on improving local transport links in the North and the Midlands.
As well improving bus services, Mr Johnson will promise 250 miles of new cycle routes across England, with dozens of "mini-Holland" schemes to make town centres safer for cyclists.
Ahead of the announcement, Mr Johnson said: "Local transport connections have a truly transformative role to play in levelling up infrastructure across the country.
"Our daily journeys for work or leisure are about so much more than just getting from A to B - they are the key to accessing skilled jobs and opportunities, boosting businesses and unlocking economic growth for towns, cities and regions across this country.
"That's why improving connectivity by overhauling bus services and making cycling easier than ever is such an important step forward, to make sure every community has the foundations it needs to thrive."