Failing to boost rail capacity on an axed section of HS2 would be “an anti-growth policy”, Greater Manchester mayor Andy Burnham has warned.

Mr Burnham said the decision in October last year by then-prime minister Rishi Sunak not to extend the high-speed railway between the West Midlands and Manchester means it will be “harder to get a seat” on trains heading north once HS2 opens.

That is because HS2 services are designed to be two 400-metre units joined together but this will be too long for many conventional stations.

HS2 services running on existing tracks to Manchester will also be slower than Avanti West Coast’s Pendolino services, as the rolling stock will not be able to tilt.

Asked on BBC Radio 4’s Today programme about the possibility of train services becoming worse, Mr Burnham said: “It’s barely believable, isn’t it, after the promises of the Northern Powerhouse and all of the debates about HS2, that in the kind of middle of this century, you would find it harder to get a seat on a train going north, because there would be smaller trains serving Manchester, because the HS2 trains couldn’t go at full length, and then they’d have to go at lower speeds because the tilting Pendolinos can go faster on the curvy West Coast Main Line, but not the HS2 trains, and that’s the point.

“You know, how can this country rely on an overcrowded West Coast Main Line and a saturated M6 for the connectivity between the West Midlands and the North West? But that was the effect of the decision taken last year.”

Mr Burnham added that more capacity is needed as “the big arteries up the country are already full”, adding: “If you carry on and do nothing at this point in time, this will be an anti-growth policy, because the overcrowded nature of our rail and road infrastructure between the West Midlands and the North West would be a barrier to economic growth.”

A proposal to build a new 50-mile railway line as a slower and cheaper alternative to HS2 was published earlier this month.

The coalition of private sector organisations commissioned by Mr Burnham and then-West Midlands mayor Andy Street described an alternative new line between Lichfield, Staffordshire, and High Legh, Cheshire, connecting with the proposed east-west Northern Powerhouse Rail, as a “golden opportunity”.

Meanwhile, the Times reported that a decision on whether to extend HS2 from Old Oak Common – in the suburbs of west London – to Euston, close to the centre of the city, must be made by the Government before the end of the year to avoid another increase in costs.

Two tunnel-boring machines purchased to complete the 4.5-mile stretch will be delivered by the middle of next month, according to the newspaper.

In her speech at Labour’s conference in Liverpool on Monday, Transport Secretary Louise Haigh said the Government will “get HS2 back under control and give people faith that Britain can build again”.