In his closing speech to the Liberal Democrat conference in Bournemouth, the party leader attacked "Conservative chaos" in government for leading to "unacceptable delays".

And he pledged the policy would be the "top priority" for him and his MPs in the next parliament.

Read more: Sir Ed Davey's speech featured a crude political calculation - analysis

Sharing how he lost both his parents at a young age to cancer, Sir Ed told the audience: "My family's story isn't unique. There are millions of us whose lives get turned upside down by cancer.

"This very day, across the UK, a thousand people will hear that fateful diagnosis. A thousand people, choking back tears as they try to process what it means for them.

"Far too many people are still waiting, far too long for a diagnosis, or to start treatment after being diagnosed.

"We will hold the government to account, for every target it misses and every patient it fails. We will never stop fighting for better care for you and your loved ones."

A source close to the leader said that in practice, the policy would work like the Armed Forces covenant - a promise from the nation that those who serve or have served in the armed forces, and their families, are treated fairly - to improve services.

The health secretary would be the person ultimately responsible for making sure the target is met.

Patients would be able to complain to the health ombudsman if they weren't seen within the timeframe, and it could see the government getting sued as a result.

The source would not be drawn over whether the policy would be a deal breaker in any negotiations with Labour after the election, as the party continues to avoid answering questions about any possible agreement coming from a hung parliament, saying instead that the Lib Dems were "focused on voters".

But he did reveal the cost of the plan was £4bn over five years.

Sir Ed underlined a number of health pledges the party has made over recent days during the speech - including enabling patients to see a GP within seven days and bringing in mental health MOTs for vulnerable groups.

But he also focused his ire on the Conservatives, as the Lib Dems attempt to win over voters in traditional Tory seats.

Throughout the conference, the party has hammered home its strategy of targeting the so-called "Blue Wall", with around 80 seats in their sights where they came second to the Tories at the last general election.

Policy announcements made this week designed to appeal to those constituencies included ditching their long-standing pledge to add 1p to income tax.

But the leadership failed to get support from its members to water down its housing targets, losing a vote on the conference floor after a campaign by young activists.

Read more:
Lib Dems have their tails in the air once again - just don't mention Brexit
10 conference moments that made headlines

Sir Ed said: "For the British people, the next general election can't come quickly enough. People are desperate for change.

"And while Rishi Sunak clings on, out of touch and out of ideas, our job - our responsibility - is to show the British people that positive change is possible. And that we are ready to fight for it, whenever the election comes.

"And this week, we've done just that. We've shown we have the policies, the passion and the people - not just to get the Conservatives out, but to deliver the real change people want. The fair deal people deserve."