HS2 has been a controversial project since plans emerged more than 10 years ago.

Here is a timeline of key events:

– January 2009

Labour establishes HS2 Ltd to examine the case for a new high-speed rail line.

– December 2010

A consultation on a route for HS2 from London to Birmingham, with a Y-shaped section to Manchester and Leeds, is published by the Conservative-Liberal Democrat coalition.

– January 2012

Transport secretary Justine Greening announces the Government has decided to go ahead with the project, despite concerns over its cost and the environmental impact of construction.

– November 2013

The High Speed Rail (London-West Midlands) Bill setting out the powers needed to build Phase 1 of HS2 between London and Birmingham is introduced to Parliament.

– January 2014

The Supreme Court rejects outstanding appeals by opponents of the rail scheme.

– June 2016

The National Audit Office warns HS2 is under financial strain and could be delayed by a year.

– September 2016

Simon Kirby resigns as HS2 Ltd chief executive.

– February 2017

The High Speed Rail (London-West Midlands) Bill achieves Royal Assent, enabling preparation work to begin.

– July 2017

HS2 Ltd accepts it was a “serious error” to make £1.76 million of unauthorised redundancy payments to staff.

– December 2018

Sir Terry Morgan resigns as chairman of HS2 Ltd amid criticism over his role as chairman of Crossrail, which is delayed and over budget.

– August 2019

The Conservatives commission a review into whether and how HS2 should continue, led by former HS2 Ltd chairman Douglas Oakervee.

– September 2019

A report by HS2 Ltd chairman Allan Cook says the railway may not be completed until 2040 and could cost £88 billion.

– January 2020

The Oakervee Review is widely leaked.

It finds that HS2 could cost up to £106 billion, but concludes “on balance” that the project should continue.

– February 2020

Prime Minister Boris Johnson gives HS2 the go-ahead despite “exploded” costs.

– April 2020

HS2 Ltd gives formal approval for companies to begin construction of Phase 1.

– December 2026

The first HS2 trains between London Euston and Birmingham were due to begin running by this date, but the project is behind schedule.

– 2029-2033

The current estimate for when services will start between Old Oak Common, west London, and Birmingham.

– 2031-2036

When the line is forecast to be extended to London Euston.

– 2027

Phase 2a from Birmingham to Crewe was due to open this year, but that is also delayed.

– 2033

HS2 was due to be completed by this point, with Phase 2b running from Crewe to Manchester, and Birmingham to Leeds.

It is not clear when either part of Phase 2 will be completed.