Government faces a tough task of delivering a seven-day NHS

David Cameron outlines his plans for the National Health Service

The Prime Minister has pledged to deliver a seven day-a-week health service in his first major speech since returning to Downing Street.

At a surgery in the Midlands, he said: "Our commitment to free healthcare is for everyone – wherever you are and whenever you need it".

ITV News health editor Rachel Young reports:

"I don’t underestimate the scale of the challenge in making all this happen but just as we came together as a nation to create the National Health Service nearly 70 years ago, so I believe that together – by sticking to the plan – we can become the first country in the world to deliver a truly seven-day NHS."

But if you think you've heard the promise before, you're right. Weekend and evening access to GPs was a Tory manifesto pledge not only this time round, but also back in 2010.

So can we trust the Conservatives to deliver it, as promised, by 2020? Certainly, by choosing to focus on the NHS first, David Cameron is underlining his commitment to extended hours.

And that's not surprising - given the fact voters repeatedly identified the NHS as their number one concern for the next five years.

But both the Prime Minister and the Health Secretary are under pressure to say where the extra GP's will come from - and we didn't hear that in today's speech.

Jeremy Hunt has admitted that in order to get the 5000 extra GP's the government is promising, about half of all medical school graduates would have to choose that specialisation.

But this year, the NHS struggled to fill existing GP training positions. And a British Medical Association survey of over 15,000 GP's last month found that a third of them intended to retire by 2020. So NHS England still needs to outline where those doctors will come from.

Even if the GP's can be found, they'll need paying for. Unlike Labour, the Tories pledged to provide the NHS with the extra £8 billion, over and above inflation, that its boss Simon Stevens said would be needed in the next 5 years.

But that money was needed for the service just to stand still - and doesn't cover extra pledges like 5000 more GPs. So listen closely when the Chancellor George Osborne delivers a budget next month ahead of the Autumn Statement. Because also missing at the moment are details of where that £8 billion - let alone any extra cash - will come from.

It is telling the Prime Minister has moved to reassure the public so quickly that the NHS is "safe in our hands". But by putting it at the top of his to-do-list, he is also illustrating just how tough the task of delivering a round-the-clock-NHS will be.