In the world of politics, leaks - while often unwelcome - have come to be expected.
From the surprise early release of Labour’s 2017 manifesto to the Guardian’s revelation that the government plans to drive down the number of low-skilled migrants from Europe, ‘official sensitive’ information - when obtained by unofficial means - has provided some of the biggest Westminster scoops of recent months.
HuffPost UK talked to some experts in the field about how leaks happen, why they happen and their impact, whether the aim is to discredit a political opponent or expose wrongdoing at the highest level.
“Dealing with a leak like the story in the Guardian this week can be one of the most challenging things for communications teams to deal with,” said Iain Bundred, managing director of PR firm Ogilvy and former Labour Number 10 spokesperson.
″In a case like this, a journalist can have hold of a whole, huge official document that you know very little about and it can be very, very challenging for someone like the prime minister’s spokesperson, for example, to get across it and know how to deal with it straight away.”
Last year Theresa May ordered a crackdown on leaking, with cabinet secretary Jeremy Heywood writing to senior officials informing them the prime minister had demanded urgent action to tighten security in Whitehall.
The memo - which, ironically, was leaked - referred to a “spate of leaks and unauthorised briefings” which had appeared in the media on Brexit, the US elections and the Autumn Statement.
“Leaking is corrosive and undermines trust and good government. Leaks are never acceptable but the regularity and cumulative impact of recent incidents mean we must now collectively take exceptional action,” Heywood wrote.
However, an “inquiry” into the leaks yielded little - suggesting attempts to clamp down on the sharing of sensitive information have no teeth - or that the culprits are too difficult to identify.
One ex-government source told HuffPost UK: ”The number one reason for leaks is news management.
“You might have a really exciting announcement that is about to launch that week, but if you brief something into the Sunday papers, preview some other aspect on the Monday, launch the policy on the Tuesday and have a follow-up on the Wednesday, you’ve got nearly a week’s worth of stories straight away.
″Another reason you might leak is to forge good relationships with journalists. You give them something which is in your interest to make public and they look good in front of their editor, who can see they are trusted and respected by their contacts. It’s a virtuous circle, if you like.”
But there is understanding, they said, that some highly sensitive information is never shared.
“It’s an unwritten rule that you don’t leak market sensitive information, or something that is really critical to the economy.
″But you could unearth a really shocking or interesting piece of information to move on an unhelpful news cycle. If a negative story has been hanging around for days, then the Lynton Crosby ‘dead cat’ method can be a good way to shake things up.”
Such a shake-up can be more wide-ranging than those responsible for a leak may realise, according to Dave Penman, general secretary of the First Division Association, the union for senior public service workers.
″It is really important to distinguish between leaking and open government and transparency,” he told us.
“There are processes in place for everyone, from civil servants to private secretaries, to raise concerns if they feel there is any impropriety around a policy that is being put forward.
“Leaking is almost always done by politicians and those closest to them for political gain, whether that’s within their own party or between two parties.
″But the impact this can have on civil servants is huge. Leak inquiries rarely yield a name because it is so difficult to identify the guilty party.
“The finger of suspicion often points to those who have played a key part in the development of a policy - usually civil servants - and I know of some people who have been forced to leave departments because they have felt tainted by a leak inquiry.”
Penman said politicians caught leaking should face the same sanctions as government workers.
“A civil servant caught leaking information would be sacked,” he added.
“Civil servants know this, which is why a department at the centre of a leak inquiry can be completely debilitated, with staff put under immense pressure.
“But politicians do not face the same threat.”
Theo Bertram, a former Labour Downing Street adviser, said some leaks are not really leaks at all.
“For example, when we were in government, we might struggle to get anyone to write up our critique of the Tories’ latest policy, but if the same information was packaged inside ‘a leaked secret internal memo to Labour’s campaign chiefs’ that made it sexy enough to be news,” he added.
“And then there are nasty, deliberate, harmful, selfish kinds of leaks. There is rarely any doubt about who did it or why: back-stabbing, butt-covering or to bounce someone into a decision.
“Towards the end of the 2010 election campaign, one of the senior figures leaked something in order to start pinning the blame for the impending defeat elsewhere. We all knew it was him. He might as well have signed it.
“Nonetheless, on the day of the leak, he bounded angrily into campaign HQ and made a theatrical scene in front of Peter Mandelson and the campaign team of lecturing me on why leaking was bad.
“After he had finished there was a short, stunned silence. ‘Well,’ said Peter, staring in amazement at his colleague’s brazen display of duplicity. ‘I think we’ve all learned something today, haven’t we.’
“And mostly that’s true: all that leaks do in the long run is show you which shits are not to be trusted.”
Leaking operations were stepped up during the five-year period in which the Tories and Lib Dems were in coalition - the most prominent of which saw plans to scrap the 50p tax rate for the highest earners revealed before budget day.
An insider said some Tories were still “understandably furious” about the incident.
They added: “In coalition there were leaks, sometimes to help one side get leverage on a policy issue, for example to get backbenchers up in arms to help kill off an idea. But you can’t just leak everything - it makes governing totally dysfunctional and it just means everything you do will also get leaked so basically everyone loses. Both sides would talk about it as mutually assured destruction.
“But for some Lib Dems the thought of that [tax plan] being announced by Osborne as the big budget day surprise was just too toxic and, frankly, the idea that the omnishambles budget would have been saved if a tax cut for the richest had been kept as a surprise is...optimistic.”
While the to-ings and fro-ings of Westminster politics might leave those outside the ‘bubble’ cold, leaks by whistleblowers have unearthed huge national stories over the years, including the Mid Staffs Hospital scandal and the revelation thousands of construction workers had been blacklisted by leading firms.
Seamus Dooley, acting general secretary of the National Union of Journalists, said the sharing of information with reporters is “essential to reporting in the public interest”.
He added: “There have been countless examples, including the Panama Papers, MPs’ expenses and Snowden’s NSA disclosures. These leaks have changed the course of government policy and public debate.
“The decision as to whether leaked information should be published or nor is determined by as assessment of the public interest, not whether publication is a matter of political inconvenience.”
During parliamentary debates on the government’s digital economy bill, the NUJ won assurances from ministers that the legislation would offer safeguards to journalists sharing information in the public interest.
“We hope the government recall this commitment in the ensuing debate about the post-Brexit immigration plan leaked this week,” Dooley said.
Bosses at Public Concern At Work, the whistleblowers’ charity, say they have been involved in a number of cases in which those who have unearthed unscrupulous behaviour have subsequently been subjected to blacklisting by a regulator; manipulation of crime figures in the police; and courtroom battles with the NHS.
Head of policy Andrew Pepper-Parsons said: “Whistleblowing is a good thing and we work hard to encourage organisations to think the same; but we’re some way off from where we want to be.
“We want to see better outcomes for whistleblowers who need to be commended not condemned for speaking up.”
Officially, the legal threshold a whistleblower must pass to qualify for protection is lower for disclosure made to an employer or a regulator than to the press or a media organisation.
“There is a grey area within all this, which is whether a disclosure to the media is a leak or an act of whistleblowing,” Pepper-Parsons added.
“In theory, the distinction is that whistleblowing is designed to expose wrongdoing, while a leak is designed to further a political aim or argument.
“From here whistleblowing is seen as an act made in the public interest, whereas a leak can severely damage the trust between civil servants and government ministers.
“In practice, this definition and whether a disclosure to the media is justified will depend on the circumstances leading up to the disclosure and whether the person making the disclosure has tried to resolve the issue via other means.”
PCAW runs a whistleblowing advice line, which receives 2,000 calls a year and can be contacted on 020 3117 2520.