The NHS waiting time target is 18 weeks from referral
Hospital patients in England will get the legal right to be seen privately if they face NHS delays.
Hospitals have to start treating patients within 18 weeks of referral - or two weeks in the case of cancer.
But ministers will now give patients a legal right to private care - or treatment at another NHS centre if so desired - if this does not happen.
The Tories, who would scrap waiting time targets, said it was an "unaffordable and uncosted" pledge.
RIGHTS OUT FOR CONSULTATION
Ministers will ask the public whether they should get a legal right to:
Choose to die at home
Access NHS dentistry
Personal health budgets
Choose a GP practice offering extended access to evening and weekend appointments
Key diagnostic tests for suspected cancer patients within one week of seeing a GP
Announcing the plans at a press conference on Tuesday, Health Secretary Andy Burnham also said everyone aged 40-74 would have a legal right to a five-yearly NHS health check from 2012 to assess their risk of heart disease, stroke, diabetes and kidney disease.
The guarantees, to come into force in April next year, will be set down in the NHS Constitution.
Mr Burnham said ministers were also considering whether to give patients a legal right to chose to die at home, and to access an NHS dentist.
These potential measures - alongside others - will be put out for public consultation.
Some patients - in fact several thousand a month - are already being treated at private hospitals under the NHS through the patient choice initiative.
This is another attempt by Labour to use the NHS as a political football
Andrew Lansley Shadow health secretary
At the start of the referral process, they are able to choose from an approved list of providers that are willing to carry out the treatment at NHS cost.
But the new rules will allow patients to opt to switch to private care at a later date if it turns out the NHS cannot see them within the deadline.
In theory, this has already been possible during the drive to cut waiting times since Labour came to power.
However, it has been incumbent on trusts themselves to arrange such steps, meaning it has not been routinely done.
And since most waiting targets were met, there was little need to take such action in the first place.
But the government believes that by introducing a legal right it will empower patients to hold the health service to the shorter waiting times which have now been achieved.
Mr Burnham said: "With this new power behind them, patients can be certain that they will receive the same high standards of care, regardless of who they are or where they live."
Prime Minister Gordon Brown said: "Every single person who has to go into hospital or go through the difficulty of cancer will have clear rights and real power guaranteeing them quick access to care, or the offer of going private or to another NHS provider if these standards are not met."
The Conservatives have said they would scrap the 18-week target, preferring to concentrate on outcomes, such as deaths, rather than processes.
Shadow health secretary Andrew Lansley said: "This is another attempt by Labour to use the NHS as a political football.
"It is the latest in a series of unaffordable and uncosted pledges that have more to do with electioneering than improving the NHS."
Liberal Democrat health spokesman Norman Lamb said: "It's absolutely right that every person should have the right to private treatment, paid for by the NHS, if their local hospital can't provide it when they should.
"But the government's announcement has a gaping hole in it for those who still aren't covered by the current target regime, such as mental health patients."
The British Medical Association also said it had concerns.
Dr Mark Porter, of the BMA's consultants committee, said: "Clearly the NHS has made huge progress in cutting excessive waiting times.
"However, many doctors remain frustrated by examples of political targets being prioritised over the needs of individual patients.
"If one group of patients gains a legal right by virtue of how long they have waited, there is a risk that others with more serious conditions will wait longer.
"We also have concerns that this will mean more NHS work going to private providers, with destabilising effects on hard-pressed NHS services."
Nigel Edwards, of the NHS Confederation, which represents over 95% of NHS organisations, said: "It is a major departure for a government in this country to guarantee what patients can expect through legislation.
"As with all new policies, it is vital to be wary of any unintended consequences - particularly around how meeting the target might affect other local health priorities for primary care trusts - once it is put in place."
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