The next few months will be "critical" for the government's NHS reform programme, the prime minister has said.

At his monthly press conference, Tony Blair indicated that his remaining time in Number 10 would coincide with the conclusion of the current phase of health service changes.

He admitted that the NHS faces "tremendous challenges" but rejected claims that standards are falling and thousands of jobs are being axed.

"The key driving force behind the changes that are happening in the NHS today is the need to deliver healthcare in a different way in a changing world," Blair told journalists.

"And we have got to hold our nerve and see these changes through, particularly over the next few months.

"The next few months are going to be absolutely critical as to whether this happens or it doesn't happen."

But Blair denied that the message to patients was "hospitals are closing, so get used to it".

He also said that the government's health service reform agenda was "important as a long term issue for the country".

He said that the NHS had been through a "crunch period" and accepted that there are "tough and difficult decisions being taken".

But the aim is to get to a situation where the amount of time people wait for their operations "is genuinely transformed".

He highlighted the government's 2008 target of an 18-week maximum wait for in-patient and out-patient combined.

"And effectively that will mean you have booked appointments and an end to waits, certainly in the traditional sense, within the National Health Service," he added.

Blair also said that changes such as the contestability of services, payment-by-results and "different ways of working" were important reforms.

Improvements could be seen in falling waiting times, he added, pointing out that most cataract treatments are now carried out in two months.

Suggestions that NHS productivity has fallen and that the government's extra spending is not being put to best use were also rejected.

"If you include quality of care within the figures - ie saving lives, improvements in waiting time, improvements in prevention and keeping people out of hospital - then actually productivity has risen in the NHS over the past few years," he said.