By 2008 patients should be treated within 18 weeks

The King's Fund said reforms such as patient choice and payment by results, whereby the NHS is paid per patient treated, may undermine the push.

By 2008, each patient should be being treated within 18 weeks of being referred by a GP.

The Department of Health said the NHS was "more than capable" of meeting the target.

The health service is currently on target to ensure everyone is treated within six months by the end of the year, but that is only from diagnosis.

The 18-week target was introduced last year after criticisms patients were facing long "hidden waits" for diagnosis.

What we need is flexibility so that patients are treated according to need, not some political target Shadow Health Secretary Andrew Lansley

The King's Fund said there were reasons to be optimistic that the 2008 goal would be met.

But the report said reforms such as patient choice - which will mean that from the end of the year patients can choose from up to five hospitals for treatment - and payment by results could be "destabilising".

And it warned the government needed to address inequalities in care - recent studies have shown variations in the treatment of heart disease and cancer across geographical and gender groups.

However, the King's Fund acknowledged huge strides had been made on hospital waiting.

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When Labour came to power in 1997, 1.3m people were on an NHS waiting list, with the maximum waiting time at 18 months.

The number now stands at just over 800,000 and only three people are waiting for longer than a year.

'Market mania'

King's Fund chief executive Niall Dickson said "nothing should be taken for granted".

"The sheer number of patients to treat, the worsening financial climate, the uncertain impact of payment by results and choice, and shortages in staff all present real challenges."

Liberal Democrat health spokesman Steve Webb said the government's reforms could create a "market mania" that would increase waiting times.

"Shopping around by patients makes it hard for hospitals to plan carefully or make best use of precious resources."

And Shadow Health Secretary Andrew Lansley said ministers were wrong to target waiting lists in such a way.

"What we need is flexibility so that patients are treated according to need, not some political target."

The Department of Health said the 18-week target was challenging, but one which the NHS was more than capable of meeting.