Image copyright HS2 Image caption Major work has already been carried out at sites such as Euston, Solihull and central Birmingham for HS2

Prime Minister Boris Johnson has given the go-ahead to HS2, the high-speed rail link connecting London to Birmingham, Manchester and Leeds.

The infrastructure project, currently the largest in Europe, has been delayed and faced mounting concerns over the exact route and spiralling costs.

While the whole line will be built, the government is set to review spend on the project to find savings.

So what is the proposed route and why has the project gone over budget?

What is the HS2 route?

The new railway line running between London and the West Midlands would carry 400m-long (1,300ft) trains with as many as 1,100 seats per train.

The line would enable trains to reach speeds of up to 250mph and would run as often as 14 times an hour in each direction.

A V-shaped second phase would then run services from Birmingham to Manchester and Leeds.

The Department for Transport has said that the project will triple the capacity of trains across the entire route.

The government launched a review of the high-speed rail network in August 2019 to consider whether and how the project should proceed. In January, the BBC revealed that it "strongly" advised against cancelling the project.

On Tuesday, the prime minister said that there would be new "delivery arrangements" for the sections to Leeds and Manchester.

Image copyright Bennetts Associates Image caption HS2 platforms in Manchester Piccadilly would be covered by a folded roof

A new HS2 station would be built next to Manchester Piccadilly under this part of the plan. City mayors in northern England have previously urged that the project be delivered in full to help boost investment and productivity in the areas.

The programme originally began under the Labour government in 2009. It is the second High Speed rail project after High Speed 1, which links St Pancras International and the Channel Tunnel, and opened in 2003.

When will HS2 open?

The first phase of the railway - between London and Birmingham - was due to open at the end of 2026.

But Transport Secretary Grant Shapps said in a written statement to Parliament in September 2019 that it could now be 2028-2031 before the first trains run on the route.

The second phase to Manchester and Leeds was due to open in 2032-33, but that has been pushed back to 2035-2040.

How much will HS2 cost?

The official price tag for HS2 was set out in the 2015 Budget and came in at just under £56bn.

However, the government estimate for the project has since almost doubled, with the latest figure rising to £106bn, according to an official review leaked to the Financial Times in January.

Image copyright Siemens/ PA Image caption A proposed design for an HS2 train

Prime Minister Boris Johnson recently criticised how much money had been spent on the project in an interview for Sky Kids' FYI show.

He said that HS2 Ltd had "just wasted money. And the whole way it was managed was hopeless."

Why is HS2 over budget?

Management issues and unrealistic land valuations have caused the cost of HS2 to spiral.

HS2 will cut through a crowded landscape. The initial stretch from London Euston to west London will be through a giant tunnel underneath central London.

Former executive Doug Thornton previously told BBC Panorama that initial estimates for acquiring property and land were "enormously wrong".

A 2019 freedom of information request revealed that property costs are forecast to reach £5bn, compared to the original £1.1bn estimate.

HS2 also failed to carry out extensive soil surveys, which has caused problems for digging and excavation, according to the project's current chairman, Allan Cook.

What about HS2 journey times?

The Department for Transport says the project will cut Birmingham to London journey times from one hour 21 minutes to 52 minutes.

Once the second phase is complete, Manchester to London journeys would take one hour seven minutes (down from two hours seven minutes), and Birmingham to Leeds 49 minutes (down from two hours).

The government hopes it will also free up capacity on overcrowded commuter routes.

What about opposition to HS2?

Some MPs argued that the construction of HS2 would create thousands of jobs.

Others believe that it could be a catalyst for economic growth and could help rebalance the economy between the North and South.

Image copyright Reuters

However, HS2 will pass through about 70 parliamentary constituencies, and local groups opposed to the scheme have lobbied their MPs to vote against the plans.

There is political pressure on some Conservative MPs in particular, some of whom oppose the project as the route will pass through their constituencies.

Some recently-elected Conservative MPs, representing seats in the north and the Midlands, are also reportedly against the project on the grounds that the money would be better spent improving local transport links.

Pressure group Stop HS2 believes that the operation of the line will cause increasing carbon emissions, as well as damage to areas of natural beauty and the ecosystems they support.

HS2 Action Alliance has previously argued that it believes a disproportionate number of the 30,000 jobs created around HS2 stations in phase one will be in London.