David Cameron has said he does not care if he has to "take a hit" on the controversial health reforms, there is no going back.
Addressing the Conservative spring forum, the Prime Minister said the shake-up was "unavoidable and urgent".
However he sought to reassure party activists over the crucial doorstep election issue of the NHS reforms, saying that the National Health Service was "in the party's DNA and that's not going to change".
Mr Cameron chose a classical rally cry to appeal to Tory grassroots at the central London event, saying "fortune favours brave governments".
He argued it was right to take "tough decisions" in a range of areas for the good of the country, including agreeing to go ahead with plans for a high-speed rail link between London and the North that will carve up key Tory heartlands.
At that point one party member cried out 'No.'
Cameron was quick to respond: "Oh, yes it is."
The event comes a day after Mr Cameron was forced to admit he rode Raisa, the ex-police horse loaned to former News International executive Rebekah Brooks.
Jokingly he told the conference he had been for a ride this morning with Mayor of London Boris Johnson, before adding it had only been on the underground.
The pair had been on a visit Transport for London's surface transport and traffic operations centre in Southwark.
Mr Cameron went on to tell activists that government cuts were being made because the party "cares" about the country.
"People say Conservatives in government are taking tough action because they don't care," he said.
"But the opposite is true. We're taking those decisions because we do care."
He insisted that pushing he is not pushing ahead with reforming the NHS "because it's easy, let alone popular" but because it is "right"
"In fact more than that, it is unavoidable and it is urgent.
Cameron said that the NHS is suffering an "invisible crisis" that if left unaddressed "will not cope under all that weight in the years to come."
"Sooner or later the cracks would have started to show. Queues would have grown. Patients would have been let down.
"So frankly I don't care about taking a hit.
"I care that it works to avert that crisis, to make the NHS strong enough for the future.
"That's why we're making, what at heart, are some pretty simple changes."
Urging the party to be bold, he added: "We didn't campaign for 13 long years just to get into government then stick it on cruise control.
"We came in to change the country we love in many ways, we came in to save the country we love.
"And there is only one way of doing that, taking tough action, putting country first, striving to the last."