Oxford Street risks losing its reputation as a shopping destination unless a scheme to pedestrianise the traffic-choked thoroughfare is resurrected, the London mayor has told the council that ditched the proposals.

In an escalation of hostilities between the mayor’s office and Westminster council, Sadiq Khan castigated the local authority for wrecking the plan “unilaterally, with no attempt to compromise”, and with no coherent proposals of its own.

Pedestrianising Oxford Street, which is closed to private cars but a heavily polluted route for buses and taxis, is one of the Labour mayor’s flagship promises, with his office drawing up a detailed plan for how this would happen.

However, earlier this month, the Conservative-run council said it could not agree to the proposals, citing the concerns of some local residents.

In a letter to Westminster’s leader, Nickie Aiken, Khan said Oxford Street’s success was of significance to London and the UK as a whole.

“Instead, it is blighted by overcrowded and poor-quality public realm, heavy traffic and the attendant problems of pollution and road danger,” he wrote.

In the era of internet shopping, the continued prominence of the street as a shopping destination could not be taken for granted, he warned. “We are all aware of the structural changes facing the retail sector,” Khan wrote, noting the imminent closure of House of Fraser’s flagship store on Oxford Street.

“Ultimately, the risk of not proceeding with ambitious and meaningful change is a risk to London’s future competitiveness on the national and international stage,” he said. “This has implications not only for the businesses of Oxford Street, but the economies of London and the UK, and ultimately all of our constituents.”

Arguing that consultations on the scheme had come out in favour of it, Khan said any new proposals put forward by Westminster would have to tackle the problems faced by Oxford Street, among them poor air quality and road safety. There are an average of one death and 60 injuries a year on the street.

Crowd levels are “uncomfortable and deters visitors”, the letter warned, saying this will worsen when Crossrail trains trains start serving the area in December.

Khan concluded: “I need to understand what you intend to deliver for Oxford Street and how it will tackle the challenges set out above.”

The pedestrianisation plans, which would have ended east-west traffic along the street, although some north-south routes would still have crossed it, were criticised by some residents over fears it would merely displace traffic to nearby streets.

They also faced concern from cycling groups for making no provision for bikes to use the road.

Khan and Westminster have also fallen out over the council’s decision to try to block a new cycle route via a judicial review, despite it being supported in a public consultation.