The head of security at the Treasury did not bother to investigate a series of "leaks" which led to the prosecution of a Sun journalist.
Senior civil servant Richard Lester also admitted he was often not sure what was a "leak" and what was a legitimate briefing, the Old Bailey heard.
Whitehall editor Clodagh Hartley, 40, is accused of paying £17,475 over more than three years to HMRC press officer Jonathan Hall for a series of stories.
Hall, 43, arranged with the journalist to transfer the sums to his personal account, before switching to his girlfriend's bank in an attempt to cover his tracks, it is claimed.
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Hall's partner Marta Bukarewicz, 45, is in the dock after agreeing to receive the payments, jurors heard.
Both Hartley and Bukarewicz deny conspiracy to commit misconduct in public office.
The court heard that Hartley did not write any of the articles in question.
Lester, head of security at HM Treasury for the last seven years, was asked for his definition of a leak.
"A leak is any incident that undermines the trust between the government and the public, between ministers and the civil service, government departments and their stake-holders, which may be other government departments, or any institution with which is operates," he said.
"It is always unauthorised.
"The underlying principal is that established in the Civil Service Code, which is that officials will behave with integrity and keep official information away from those who do not need to know it."
Lester said the main annual government budget was subject to particular secrecy.
He said secrecy was important because "people could react to interim proposals when they are not going to form part of the final budget".
Lester added that although government press officers were important in disseminating the budget, they only became involved "towards the end" of the process.
Prosecutor Zoe Johnson asked Lester to discuss six Sun articles, which he had been shown earlier by police.
Johnson asked Lester to comment on whether information contained in the articles was "generic" or "specific".
She also asked him to consider "whether anything about the publication of those specific articles had any capacity to undermine the budget itself".
The first article was a spread on Alistair Darling's last budget, headlined "Don't fudge it" and printed on Budget Day, 24 March, 2010.
Accurate predictions about Darling's speech included increases in fuel, alcohol and tobacco duty as well as the abolition of stamp duty for some properties.
Lester said: "These are specific. That is information that would not have been made public until the Chancellor had announced it…I think he started speaking after Prime Minister's Questions at about 12.30 on the day, some time around that.
"It does undermine the process, yes, because it is information that is held back until the budget speech, because it could influence people to rush out and buy alcohol, buy fuel and [cause] a subsequent loss to revenue to the government."
Lester was next shown an article which appeared two days after the budget about a £20 billion black hole in the government's books.
He said: "It is outside the budget process so information in there relating to the budget is in the public domain by that time."
From 24 May 2010, the witness was shown the article, "Child trust funds axed", which predicted the change was to happen "today".
Lester said: "There are specific elements [in the article] so there is potential undermining, albeit this is outside the specific budget period, but very close to a new government coming to power.
"We would not like figures to get into the public domain before they are finally released, because until they are released people might change their mind – sorry, the government might change its mind."
The fourth article, on George Osborne's first "emergency budget", was printed on 24 June 2010, two days after the Chancellor's speech.
Lester said: "The majority of this information was already in the public domain."
He said it contained data "publicly available to everybody immediately the Chancellor has finished speaking".
"This is not classed necessarily as a leak."
The penultimate article, "1 in ten get axe", was printed on 20 October, 2010 and discussed civil service cuts.
It was printed on the day of the Coalition's comprehensive spending review, the day after Chief Secretary to the Treasury Danny Alexander accidentally revealed the planned jobs losses to a photographer outside Downing Street.
Lester said: "Any information which could be seen then [in the photographed document] could have been picked up and published, from the data that was seen.
"Anything that was not made available in that picture to the paper and was contained in that articles would be a leak…"
The civil servant failed to point to any specific point in the article he alleged was a "leak".
The final article, "Fuel good factor", was printed on 23 March, 2011 and revealed George Osborne would not increase fuel duty in his budget.
A sidebar also revealed "MOT tax blocked for now".
Lester said: "This is detail which would have been planned in the budget and therefore would only become public knowledge when the Chancellor had spoken about it in Parliament…he would have begun speaking at about 12.30."
Johnson asked what the effect of this article might have been.
"In this case, you are talking about fuel tax, so early notification.
"Naturally, the public would rush out to get fuel before the tax came into effect."
Johnson asked if the Treasury had investigated any of the supposed leaks at his behest.
"No, they did not", Mr Lester replied.
Johnson asked finally, if the articles had had any "impact on relations between HM Treasury and HMRC".
"The articles did not", Lester replied.
Referring to the "Fuel good factor" story, Alexandra Healy QC, for Hartley, pointed out that George Osborne had provided a quote in response to the "Keep it down" campaign against fuel duty rises.
Healy said Hartley had not even written the article about fuel duty – it was penned by Steven Hawkes and a reporter who cannot be named.
She went on to say that the planned fuel escalator, put in place by Alistair Darling, was a matter of public record.
Lester agreed he had been "misspeaking" when he talked about a potential rush on petrol.
"I am sorry, I am misreading it," he said.
Hartley had only written the sidebar, accurately predicting an MOT tax would not be introduced.
Healy questioned Lester generally about the role of Special Advisers, and ex spin doctors Charlie Whelan and Damian McBride, both of whom have confessed to leaking sensitive info to journalists.
Lester said his role had been made increasingly difficult, since "SPADs" could brief journalists with relative impunity, at the behest of their "political masters".
"Sometimes items that are briefed are called leaks and identifying whether they are or are not can be extremely difficult."
Both Hartley and Bukarewicz deny conspiracy to commit misconduct in public office.
Hall has accepted he supplied stories for which he was paid.
Bukarewicz, of Grafton Road, Kentish Town, north London, and Hartley, of Brockley, south east London, deny conspiring to commit misconduct in a public office.
The trial continues.
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