Only 57% of people with the most serious conditions were treated within the four-hour national target when visiting a London North West Healthcare Trust hospital.
The report, published on Monday (November 6), suggests north-west London has the highest number of people attending hospitals (27%) out of all regions in the country.
It also found that the trust has the second-highest A&E admissions in the capital and treated 11,272 people with the most serious conditions in A&E in September.
On top of that, north-west London was the worst region in the capital when treating patients with the most serious conditions within the national target.
A decision to close the blue-light A&E services at Ealing Hospital is expected next year, after the hospital had its maternity services taken away in July 2015.
While there will be a GP-run urgent care centre at the hospital, residents could face at least a 40-minute journey on public transport to their nearest accident and emergency department.
A spokesman for Ealing Council said on Monday (November 6) the findings show the region is already “struggling to cope with patient demand”.
With north west London having the worst performance record out of the capital's five regions, he said the findings “heavily support the need to keep vital health services”.
Council leader Julian Bell said: “We have excellent doctors and nurses working in our hospitals and this performance doesn't reflect their commitment to their patients.
“It shows a system buckling under the pressure of increasing demand from a growing population.
“How will hospitals in the area cope with the removal of two busy A&Es and the loss of 500 beds?"
Statistics also found performance for patients with the most serious conditions deteriorated sharply at the trust from 68.2% in August to 57% in September.
'We will do everything to fight these plans'
Cllr Bell added: “These figures are very concerning considering we have not yet reached the peak winter season when you would expect to see a rise in the number of people seeking A&E treatment.
“Some of the country’s leading health experts have raised serious concern about what is proposed in our area and so I have written again to Jeremy Hunt, the secretary of state for health, to ask him to scrap these plans.
“We have lost two A&Es in the region already and cannot take any further cuts to our A&Es.
"We will do everything possible to fight these plans and safeguard these vital health services for our residents.”
Responding to the statistics, Lee Martin, chief operating officer at the trust, told getwestlondon they are investing £800,000 into A&E more in Ealing and Northwick Park Hospital ahead of winter.
He said: “Our aim is to always see and treat patients attending A&E as quickly and as safely as possible.
“As the second busiest trust in London our staff continue to work incredibly hard under difficult circumstances and September’s A&E figures reflect the ongoing challenges seen across the entire NHS.
“Along with other hospitals in London and nationally, we have been experiencing pressures due to the number of acutely ill people arriving at our A&E combined with much higher numbers of frail older patients who require social support to be discharged from hospital.
“The solution to reducing waiting times cannot be done in isolation and we continue to work closely with local health partners to ensure patients are being treated and cared for in the most appropriate facility, be that in hospital or in the community.”
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