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Rishi Sunak has defended his plan to axe the HS2 high speed rail line to Manchester, criticising the “enormous” cost of the project and saying he was prepared to take tough decisions.

The UK prime minister is expected to announce the scrapping of the Birmingham to Manchester leg of HS2 in his Conservative party conference speech on Wednesday, switching billions of pounds of savings into other transport projects in the north and midlands.

In a series of media interviews on Tuesday, Sunak declined to comment on “speculation” but ministers, Tory officials and industry executives say he will kill off the northern leg of HS2 on Wednesday.

Sunak said the project costs were “enormous” and equated his deliberations on HS2 with his decision to axe some of Britain’s net zero targets last month on cost grounds.

He also confirmed that he saw the HS2 line to Manchester as less important than improving rail links between northern cities across the Pennines. “East to west is the biggest concern most people have,” he told Times Radio.

Sunak has baffled and dismayed Tory officials by allowing uncertainty over HS2 to dominate the party’s conference in Manchester, and the issue again dogged him on his Tuesday morning broadcast interviews.

“I will take the time, go over it properly and make sure we take the right long-term decisions for the country,” he told the BBC. Sunak said he would not “take the easy way out, chase the headlines”.

Aides have not denied that Sunak will announce his new transport plan on the podium on Wednesday, but officials have been working frantically behind the scenes on a plan B.

The prime minister knows that any new schemes announced at the conference will be studied forensically, with experts likely to point out that their delivery could be many years away.

Downing Street declined to comment on whether the HS2 line from Birmingham to London would terminate at Euston or at Old Oak Common, six miles from the centre of the capital. Sunak’s allies described as “speculation” a Times report that the line to Euston would be reprieved.

Andy Street, Conservative mayor of the West Midlands, on Monday accused Sunak of “cancelling the future” and undermining investor confidence in Britain by aborting the country’s most high-profile infrastructure project.

“If you tell the international investment community you are going to do something you bloody well have to stick to your word,” he said at a meeting on the fringes of the conference. He has declined to say whether he might resign over the issue.

Aides to chancellor Jeremy Hunt did not deny that he had already approved the radical scaling back of the HS2 project. “A decision will be announced in due course,” said one.

One minister said: “It is incredible this has dragged on for so long. It has dominated everything.” One Tory official said it was “suboptimal” that Sunak planned to scrap a high-speed rail line to Manchester in a speech delivered in Manchester.