The NHS is facing a far greater demand for services than there funds available, Dr Mark Porter, chair of the BMA council, has warned.
Funding particularly is stretched for emergency medicine and general practice, with waiting targets being missed.
The warning has been issued as he goes before the NHS Select Committee this afternoon to highlight the funding problems facing the NHS.
Porter said: "The NHS is going through its tightest funding squeeze in half a century. While investment has stalled, demand on services is rising and a massive funding gap is opening up.
"The NHS has reached a crossroads - it is a reflection on just how hard front-line staff are working that the quality of patient care has so far been protected, and indeed improved, despite years of underinvestment, but pressure on services is now at a critical point and cracks are beginning to appear.
"For patients this means unacceptable waits for treatment, the worrying rationing of care and longer queues in our GP surgeries and emergency departments.
"While greater integration of care, investment in preventative care and reforming the financially crippling PFI system are needed to deliver savings in the longer term, we cannot escape the fact the NHS is - at this moment - in dire financial straits.
"With the election looming there needs to be an urgent and honest public debate about what the NHS can afford to deliver with current levels of investment."
He added: "We cannot continue to meet rising demand with underinvestment, and if we want to maintain universal healthcare then, put simply, the NHS needs more money. It's not too late to turn things around, but if we don't act now it soon will be."
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