The warning comes as analysis from the Health Foundation think tank showed that 4.7m fewer people were referred for routine hospital care in the first eight months of 2020 compared with the same period last year as the COVID-19 pandemic disrupted NHS services.
The drop represents a 34% fall in referrals for routine hospital care such as hip, knee and cataract surgery, the report authors warn - driven by patients' reluctance to come forward early in the pandemic and the suspension of hospital services as staff were diverted to manage COVID-19 cases.
Some 4.2m patients are already on NHS waiting lists for routine elective care, with around half waiting more than the 18-week standard - and the think tank has warned that the missing referrals from earlier in the year will compound pressure on the health service.
COVID-19 second wave
Hospitals are again struggling to maintain services in the second wave of coronavirus - with the Queen Elizabeth hospital in Birmingham last week announcing the cancellation of all planned procedures to cope with a surge in 'very sick' patients.
Liverpool LMC medical secretary Dr Rob Barnett said the NHS backlog was having a significant adverse impact on primary care.
He told GPonline: 'With hospital appointments being cancelled or delayed, care isn’t flowing through the system as normal - workload in primary care has gone up because practices are dealing with patients who would ordinarily already have been seen in hospital.'
Dr Barnett said a colleague had recently carried out repeated consultations over a four-week period with a patient waiting for assessment of a mental health condition that would 'normally have happened within a week'.
Patient care was delayed 'across the board', he warned: 'People are waiting for orthopaedic assessment, hip replacement, issues with sexual health services - it's right across the board and the backstop is as always is general practice.
'GPs are used to carrying quite a heavy clinical workload anyway, but the fact they are consulting with the same patients more frequently is adding to the stress and strain - and as time goes by these patients' conditions deteriorate, which has an added effect on the overall intensity of the work being shouldered by GPs.'
The Health Foundation researchers said their findings highlight the scale of the challenge facing the NHS as it heads into winter while managing a second wave of COVID-19 and the effects of the previous wave.
Senior policy fellow Tim Gardner, one of the report authors, said: 'While the NHS is rightly focused on the urgent task of fighting COVID-19, there is meanwhile a rising tide of unmet need which will have a significant impact on people’s health if a sustainable solution is not found.
'The NHS made significant progress towards fully reopening services after the first peak of the pandemic, but there is still a potentially huge hidden backlog, as the health service is undertaking far fewer routine procedures compared to last year.'
Commenting on the suspension of routine services at the Queen Elizabeth hospital, BMA West Midlands regional council chair Dr Stephen Millar said: 'It is incredibly concerning, that a hospital of this size is having to adopt such drastic measures at this very early stage of winter.
'Despite claims from NHS leaders earlier this week that lockdown should mean that we do not face mass cancellations, hospitals are clearly already at this tipping point. The Government must be forthcoming and deliver urgent resources to ensure that hospitals can cope in the coming months and resume care as quickly as possible.'