Health is a devolved matter dealt with domestically by the Scottish Parliament, and the Welsh and Northern Ireland assemblies. Westminster retains UK-wide powers over medical regulation and safety.
For better or worse, the ability of the party in power to reduce the number of people waiting for health care has become a key test of their competence in running the NHS.
Responding to this, Labour made a key part of its pitch to the voters in 1997 a pledge to reduce hospital waiting lists by 100,000.
And waiting lists have indeed fallen since Tony Blair entered Downing Street - but interpretation of the figures is still open to debate.
Statistics for March 2001, the last published before the election, showed the number of people waiting for a hospital admission was 1,006,600.
This represents a fall of approximately 151,000 from the 1,158,000 Labour inherited in 1997.
While the number of patients who had been waiting for more than a year in March was 4,200 lower than the February figure of 41,400, there were still 158 people who had been waiting more than 18 months.
The target was first met in March 2000.
But opposition parties say that the figures released by Labour do not tell the whole story.
They say the cut in the inpatient waiting list has only been achieved by creating a "waiting-list for the waiting-list".
The Liberal Democrats published Department of Health statistics comparing the first quarter of 1997, before the last election, to the last quarter of 2000.
These, the party said, showed that in 38 of 63 treatment specialties recorded, there had been increases in out-patient waiting lists.
Overall, the party said, waiting lists had increased by 61%.
But Labour says that statistics for the first three months of this year show a fall of 115,000 in the number of people on the outpatient waiting list.
There are also some specialties, such as paediatrics, mental illness and palliative medicine in which outpatient waits have been reduced.
The Tories have also accused Labour of using several ruses to meet their pledge.
These include taking people off waiting lists if they fail to respond to letters or dealing with easy-to-treat cases before urgent ones, thereby distorting the figures.
The waiting times initiative was started by former Conservative prime minister John Major.
He wanted to concentrate on those patients who had waited longest for treatment - and drive down the average time people spent waiting.
But many health professionals said this led to a distortion of clinical priorities, because those who have waited longest for treatment are by definition those who are in least need.
While they were in opposition, Labour bitterly opposed the policy, though they embraced it when they took office.
Instead of cutting the length of waiting times, Labour chose to cut down overall numbers on waiting lists.
An action team, headed by a waiting list supremo, which looks at new initiatives was established.
This approach has been criticised by analysts who support the approach taken by the Conservatives. They say the number of people waiting is not important - but the length of time they have to wait for treatment is.
But Health Secretary Alan Milburn maintains focusing on waiting lists is crucial, because public confidence is affected by waiting lists and cutting waiting lists will cut waiting times.
A 1997 Office of Health Economics study found there was a strong link between long waiting lists and the decision to take out private medical insurance.
In addition, the study said, the more people who took out private insurance the less support there would be for health care paid for through taxation.
The emphasis on waiting lists risked distorting priorities across the NHS as a whole, it continued, and added that waiting lists were easily measurable, whereas other services such as community mental health services were less easily quantifiable and thus may suffer.
Labour's NHS Plan
In the NHS Plan, published last summer, the government spelt out its vision for future waiting times.
A maximum out-patient waiting time of three months, and a maximum waiting time for surgery of six months by the end of 2005, with an aim to reduce that figure to three months were announced.
The government has said by next year, six out of ten patients should be able to see their GP within 48 hours and a member of the primary care team within 24 hours.
From 2002, if an operation is cancelled in the day it is due to take place, a new, binding, date will have to be offered within 28 days, or the hospital will have to fund private treatment at a time the patient chooses, they promise.
By 2004 all patients will be able to see their GP within 48 hours.
And Labour say by 2004, no one should wait more than four hours in A&E from the time they are admitted to the time of admission, discharge or transfer.
The Conservatives are committed to abolishing Labour's waiting list initiatives and say more private sector health care should be used to help treat those stuck waiting for treatment on the NHS.