Could Labour just build HS2 in full if they win the general election?

Rishi Sunak could be poised to sign off more cuts to HS2, with an announcement expected in the coming week. But if the prime minister does announce new cuts, he will do so with a rather large elephant in the room: the next general election.

An election is expected to be held sometime next year, and after it is over, if the polls are to be believed, the Conservatives will no longer be in power.

Will Sunak’s decisions on HS2, which will not see services run for many years, even make a difference if an incoming Labour government decides to take a different course?

The first question is whether Labour would even want to do things differently in relation to the high-speed rail project.

There is good reason to think so. The party’s line for years has been that it will build HS2 in full, including the full original “Y” network, incorporating a spur up to Sheffield and Leeds.

But an element of uncertainty was introduced last weekend when the party’s campaign coordinator, Pat McFadden, declined to commit to completing the project until the final costs were known.

This was rather inconvenient, as around 24 hours earlier Labour had published an official policy document pledging to “keep the promises made to the North and Midlands and deliver Northern Powerhouse Rail and High Speed 2 in full”.

And the following day, the shadow transport secretary, Louise Haigh, posted on Twitter: “Labour are committed to delivering HS2 in full and maximising its economic benefits”, apparently clarifying the party’s position.

Taking a step back and looking at the politics, it is difficult to see how Labour could fail to build HS2 without declaring open warfare on its city and regional mayors, including Andy Burnham, Tracy Brabin and Sadiq Khan – who all want the network to be completed.

But equally, the probable next chancellor, Rachel Reeves, will face many of the same cost pressures as the current government, and has so far committed to very similar spending plans.

Let us suppose, though, that Labour does decide it will build the project in full – would it actually be able to?

In theory, with a parliamentary majority, the answer is a clear yes. As the new party of government, it would be able to build what it likes. But there would be some hurdles, and what Sunak announces this week will make a difference.

Building a new railway in this country requires parliamentary legislation. The portions of the line from London to Birmingham and thence to Crewe – known as phase 1 and phase 2a – have already passed through parliament. But the section connecting Crewe with Manchester, known as phase 2b, is currently going through parliament.

There are concerns among rail industry insiders that if Sunak decided to scrap that segment and withdraw the bill, it would not be simple for Labour to reverse such a step.

The legislation would have to be reintroduced by the next Labour government and go through the whole parliamentary process, requiring parliamentary time and inevitably introducing more delays. It is not a case of simply flicking a switch.

The leg to Leeds is already in a similar situation. The preparatory design work has been done for the project, but if Labour were to recommit to it, the party would have to go through a legislative process.

There is also the matter of the technical challenges that will arise if the project is delayed. Some works need to be done in a certain order or they incur massive additional costs, which could be off-putting. And delays also mean extra costs in a broader sense – employing more staff for longer while inflation continues to rise.

This is all far from ideal for a project that has been repeatedly beset by delays and rising costs. It would certainly be possible for Labour to complete HS2 in full were the party to come to power, but what Sunak announces this week will have a real impact on what it can achieve.