“People have had their hearts broken too many times,” says a long serving Labour staffer.

Nobody in the Labour Party wants to talk about being on the brink of power at this general election, whether they are in campaign HQ, out banging on doors, or quietly tucked away hatching plans for government.

Labour is not a party, or a political tribe, that is used to winning.

There is superstition, caution, maybe even a touch of paranoia, that a general election victory could slip away somehow.

As the days count down to 4 July and polling day, “you tick off the big ticket things – the debates, the manifesto launch, the candidate selections, then there are fewer and fewer things to worry about”, says one source, adding that there has been a “slight easing of tension and anxiety”.

Another insider tells me “it’s much calmer”.

At the party’s headquarters in Southwark, south London, there is, one source says, a complete vow of silence “on any discussion of anything beyond 10pm, Thursday 4th”.

“I can’t really lay on thick enough how different the atmosphere is in HQ than elsewhere, every meeting is focused on what we need to do better, polling barely gets discussed.”

A private memo from Labour’s campaign chief, Pat McFadden, sent to candidates on Friday says “up to a quarter of voters are yet to make up their minds”.

That is way more than most of the polls suggest when they report on undecided voters, estimated to be around five million people.

But Labour takes into consideration not just the “undecideds” but also, the “uncertains”, which could make up another three million.

These are people who, if asked, tell pollsters that they have chosen which party to back, but when asked how sure they are about their choice, they swither.

By the time you factor in turnout, the estimate at Labour HQ is that there are around seven million or so voters who have not yet made their minds up. The final decisions of that huge number of people will clearly have a massive impact on the eventual outcome.

That’s why, in the next couple of days, as the campaign enters its final phase, Labour HQ will start shifting its message.

McFadden’s memo instructs candidates, in bold type, to tell voters: “Don’t stay at home. Don’t assume anything about the result. Don’t vote for a minor party which will only help the Tories. In this seat the only way to stop the Tory is to vote Labour.”

Last week, the Conservatives started to use the massive gap in the polls as a tool to warn the public about a huge Labour majority. Labour will increasingly warn the public not to believe them.

McFadden notes to candidates: “It’s one thing to have polls guessing the outcome. It’s another entirely for polls to influence behaviour – and that is the danger here. If people conclude the election is a done deal it could have the unintended impact of boosting the Tory seat count at this election…. and it is essential that we communicate to voters that nothing is decided.”

Five years ago, Labour might never have dreamed they would have such success in the polls that it could present a risk.

Those doubts about “don’t knows” are also felt by Labour candidates who have been knocking on doors.

One shadow minister said: “It doesn’t feel like only 10% haven’t made their minds up to me… there is a lot of disaffection, disquiet with politics as a whole,” voters doubtful that any politician could improve their lives.

Another candidate said: “It’s still quite hard. Lots of people do want change, but lots of people have voted Tory forever.”

That said, no Labour candidate would argue that it’s not looking good for them.

The party is pushing harder into seats where Conservative majorities are bigger and bigger.

Even voters in “massive houses” are coming over, said one Labour candidate who has been campaigning in the commuter belt around London.

They told me how canvassers had decided not to not knock on one door because the 80-year-old woman who lived there had been marked down as a solid Conservative voter for years.

But she emerged from the house “really put out” that they had not wanted to speak to her, and said she would, for the first time, be backing Labour.

“It’s the first time I have been chased down the street for a good reason!’” the candidate told me.

Others are allowing themselves to be a bit more excited. One experienced campaigner said they were “struggling with the no complacency rule”, after they had not found a “single Tory voter” in a traditional Conservative constituency.

But while the focus at Labour HQ is on getting over the line, and not dreaming of what comes next, different priorities prevail at another office up the road, sources say.

Here, a team led by Sir Keir Starmer’s chief of staff, former Whitehall boss Sue Gray, is said to be quietly preparing for government.

Labour will not confirm this officially or tell me how many people are working there, saying only that there is an “overspill” office where various teams are based.

The party is determined to avoid any whiff of taking the general election result for granted.

But significant work is under way. The teams who hope to be moving into government in a fortnight are carving out more time to plan their hypothetical first moves.

Shadow ministers and advisers have taken part in what are called “access talks” – meetings with civil servants about what they hope to do in government if they win.

One of those who’s been involved said: “The arrival of former Whitehall mandarins has made Labour more ready for government than the electorate can see.

“Detailed shadow cabinet training and policy formulation plans with outside experts has made a huge difference.”

The voting intention surveys the party worries about have helped build relationships with Whitehall, sources suggest, with one saying: “The civil service have been very receptive with a poll lead like this.”

One shadow minister told me: “You wouldn’t believe the amount of work we’ve done.”

But it’s not a process full of joyful anticipation. One insider described it as “overwhelming…the more we get into the prep for government, the more we realise the how big the problems are”.

And they know how cynical many of the public are about whether politicians can really change their lives for the better, as Labour hopes to do.

Speed and clarity would matter. Even governments only get one chance to make a first impression.

The Labour Party cannot yet let itself believe that in less than a fortnight they could be in power, that Sir Keir Starmer might be putting the finishing touches to his cabinet, preparing to fly to his first Nato summit on 9 July as Labour’s seventh prime minister – and only the fourth to win a general election.

His team knows there is still time for things to go horribly wrong.

They don’t believe the polls released to the public and don’t want you to either.

There are still difficult questions for them that so far in this campaign they have not fully answered.

How would they pay the bills if they can’t get the economy to grow?

Which taxes might they put up?

How would they significantly improve the NHS with only a limited extra cash injection to start with?

How would they support universities when they say that higher education is in crisis?

And as we have talked about so often in our studio, how would they tackle the long-term problems with the creaking social care system?

And how should Sir Keir Starmer handle questions about his backing of Jeremy Corbyn at the 2019 election, which he struggled with on Thursday in front of the Question Time audience?

Insiders acknowledge this was not his finest moment and there are still plenty of occasions before polling day when he might be asked whether he really believed that Mr Corbyn would be a “great prime minister”, and squirm.

Just as the Labour leader has been haunted by his past membership of Mr Corbyn’s top team, the party’s psyche is shaped by its own history.

Their campaign has run smoothly. The numbers all point in their direction. And they have been helped, no doubt, by an astonishing series of mess-ups from their opponents.

The Labour campaign spotted the spike in betting on the timing of the election – which the Gambling Commission is now looking into – back in May.

That meant it could start buying ad space and spending money before the election was even called.

But it’s hard to find anyone on Starmer’s side who is luxuriating in the prospect of victory.

The outcome isn’t certain, and it is simply not the Labour way.

One senior MP joked: “I won’t believe it until I see it, and even then, I might not be sure.”