The spectre of a queue of NHS patients snaking ever further into the distance as the next election approaches is one that haunts ministers. What seemed a modest pre-election pledge - to cut the queue by less than 10 per cent - has become a burden and an embarrassment.
Worse, it may be unachievable. In the four years from 1990-91 to 1994- 95 the annual number of NHS patients treated rose by 800,000 as hospitals, feeling the heat of the Tory NHS market, cranked up productivity. Yet waiting lists rose during the same period by 100,000, just as they did in the first nine months of this government.
Where did all the extra patients come from? A look at the referral patterns delivers an instant answer. GPs increased the proportion of patients they referred to a specialist by almost a third. In 1990-91, they referred just over 5.5 million patients to hospital. In 1994-95 this figure had grown to over 7.3 million.
In four years, almost two million extra patients were crowding into out- patient clinics, half finding their way on to waiting lists. Richard Hamblin, a researcher at the King's Fund, the health policy think-tank which published the figures in the Health Service Journal, says there are two explanations: either GPs were spotting more people with the same degree of need whom they had not previously referred or specialists were lowering their thresholds and offering operations to less sick people, or both.
It appears that as hospitals increased their work rates, doctors saw the opportunity to get more patients treated and upped their referral rates.
Waiting times have remained at an average of around 13-14 weeks since the 1960s, despite a doubling of the numbers on the lists. The faster patients are treated from the waiting lists, the faster new patients are added to them.
Mr Hamblin says this implies that there may be a waiting time acceptable to GPs and specialists. "If increases in activity seem likely to reduce waiting lists to below this level they refer more patients. List size and activity levels remain in equilibrium to ensure that waiting times remain unchanged."
Throwing money at the problem - the Secretary of State for Health, Frank Dobson, has allocated pounds 320m to the task in England this year - may yield short-term gains but will ultimately aggravate the problem. As doctors become aware that waiting lists are shrinking they will refer more patients.
Labour's second term could depend on whether ministers can time the short- term dip in the lists to coincide with the next election before they start to grow again, as they inevitably will.