Sadiq Khan has dumped the “Boris bus”, a key part of the now foreign secretary’s legacy as London mayor, because it is too expensive to produce. The new generation of red double-decker Routemasters, with folding doors that allow passengers to hop on and off, was introduced by Johnson in 2012, to great fanfare.

Designer Thomas Heatherwick was credited with giving the new Routemaster a modern “London look”. After the bus was first introduced, he said it was a compliment that it had so quickly become “part of London’s landscape and personality”. Heatherwick also designed the cauldron for the opening of the 2012 London Olympics as well as the so-called Garden Bridge, yet to be built across the river Thames.

At the time, the London mayor described the new bus, built by Northern Ireland company Wrightbus, as a “stunning piece of automotive architecture” representing the “very best in British design, engineering and manufacture”.

However, during the mayoral campaign last year, Khan suggested that as London mayor he would look at holding off on purchases of the new Routemaster as a way of making budget savings to help pay for a promised four-year public transport fares freeze.

It has now been confirmed in Transport for London’s business plan that “new capital investment will be reduced significantly as we discontinue purchases of new Routemaster buses”.

The move will be a blow to Johnson, whose legacy as mayor now looks increasingly slim. In March, former Downing Street adviser Steve Hilton said that he struggled “to think of what his legacy is”. Hilton added: “The real legacy of moving London’s transport system forward, I think, happened with the previous mayor, with Ken Livingstone with the big moves – the introduction of the congestion charge and the Oyster card – and in those two areas of transport and promoting London it’s really difficult to think of something specific that you could [point] at as being Boris Johnson’s legacy.”

The new Routemaster, first raised as a possible project before the 2008 electoral victory that put Johnson in City Hall, had been intended to combine cutting edge green technology with a revival of hallmark features of the original London Routemaster.

Its reintroduction, seven years after the original Routemaster had been withdrawn to be replaced by easy access low-floor buses, was also celebrated by many as a move to rid the capital of Livingstone’s unpopular “bendy” variety.

Johnson originally said he hoped there would be 2,000 Routemasters on London’s streets by 2020. Wrightbus, the Northern Ireland firm that makes them, warned earlier this year that its Routemaster production line would have to be shut down within months if no new orders were received. The original contract was to supply up to 1,000 buses.

He paid £354,000 per bus for an initial bulk consignment in 2012 of 600, and approximately £325,000 for an additional 200 in 2014. The new fleet was attacked at the time as an expensive vanity project and soon became the subject of a series of unfortunate stories, including the revelation that the batteries on a large number of them had failed. The hybrid diesel-electric technology is also now widely seen as having been superseded by electric battery technology. And in July last year, 300 London bus conductors were told they were to lose their jobs to make transport savings of £10m a year. The staff cuts mean that hopping on and off the buses is no longer an option.

Asked to comment on the move, a spokesman for Khan said TfL would instead be investing in a new generation of buses that would help to improve air quality.