The warning comes as a BMA analysis of pressure on emergency care services reveals that the NHS delivered 'worse levels of care' through summer 2018 than in five out of the past eight winters.
BMA leaders warned earlier this year that extreme pressure on the NHS last winter would continue through summer - and the union says analysis of key indicators shows fears of a year-round crisis have proven correct.
The analysis suggests the winter ahead could prove extremely challenging for the health service, with GP leaders warning that primary care could struggle to cope with a repeat of NHS pressure last winter, which saw thousands of elective procedures cancelled and drove up work for GPs.
Through July to September 2018, 125,215 patients were left waiting on a trolley for more than four hours after the decision to admit them to hospital, the BMA analysis found. This figure is greater than the figure for January to March in every year from 2011 to 2015.
In the last three winters, numbers of patients waiting on trolleys for more than four hours hit 155,277 in 2016, 177,012 in 2017 and a record 226,176 in 2018, the BMA found.
Summer 2018 saw worse performance against the four-hour A&E waiting target than each of the winters for 2011-2015, and a comparison of performance in winter 2011 with winter 2018 (January to March) showed a seven-fold rise in total trolley waits over four hours and 19% more emergency admissions.
BMA chair Dr Chaand Nagpaul said: 'These figures lay bare the long-term underfunding of emergency care services in England that have experienced years of declining budgets and staff shortages at a time when patient demand has rocketed.
'Pressure on the NHS has developed into an all-year crisis. The BMA correctly predicted that the summer of 2018 would be as bad as many recent winters.'
Londonwide LMCs chief executive Dr Michelle Drage told GPonline: 'GPs and practice teams face year-round pressure from workforce shortages and a lack of funding reaching frontline care. Last winter was not typical and if this winter is as bad as many previous ones then the dedication of GPs and practice staff alone may not be enough to meet patient demand.
'In London 3,148 elective operations were cancelled for non-clinical reasons between October to December 2017, and a further 3,744 from January to March 2018. Many of these patients then needed care from their GP while they waited for their operation to be rescheduled, a repeat of this would stretch practices to their limit.'
RCGP chair Professor Helen Stokes-Lampard said: 'This analysis showing that the NHS is facing unprecedented year-round pressures will come as no surprise to hardworking GPs across the country.
'Our emergency care colleagues are, as this analysis highlights, operating under enormous strains, but it is important to remember that GPs are also on the frontline of patient care and our profession - and our patients - are facing the impact of these pressures on a daily basis.
'Health secretary Matt Hancock has said that preventing people from getting ill in the first place should be central to how the NHS works, but first of all we need a well-funded and well-equipped primary care system. This will alleviate pressures across the NHS and allow us to deliver care in the community where it is more cost-effective, and where our patients want it most.'
An NHS England spokesperson said: 'The NHS’s extensive planning for winter is already well underway, with access to clinical advice through NHS 111 and evening and weekend GP appointments improving people’s access to care, plus action by hospitals and local councils to free up beds by reducing long stays. Staff getting vaccinated against flu will also help reduce the pressure on services over winter.'