In the address that would become his best known, Hockey criticised governments' tendency for "reckless spending" and boldly declared: "The age of entitlement is over".

Less well known – and concealed from the public until now – was that on the same day back in Sydney, Mr Hockey was sent a letter that threatened to derail his ambition to secure the second most powerful job in Australian politics at the forthcoming election.

The two-page letter advised Hockey of an "apparent fraud" against his taxpayer funded Cabcharge card involving alleged "phantom journeys" amounting to thousands of dollars.

"We intend to refer this apparent fraud against your card to the federal police," the letter from Cabcharge company secretary Andrew Skelton advised.

Mr Skelton told Mr Hockey that Cabcharge was undertaking a "full investigation of the circumstances" at the request of the then Department of Finance and Deregulation.

Documents obtained by Fairfax Media after a two year freedom of information process show in relation to Mr Hockey's account the rules for MPs using privately chauffeured hire cars were repeatedly broken.

Drivers from a favoured hire car company had filled out and signed on Hockey's behalf Cabcharge dockets worth at least $10,000, dating back to as early as 2009.

Several Cabcharge dockets from 2010 obtained by Fairfax Media state they are an "emergency docket ... to be used only in the event of failure of terminals".

Many of the dockets – for amounts as high as $760 each at $95 an hour - do not contain destination or time details, but simply state the driver transported Hockey "as directed" for up to eight hours at a time.

Some show Mr Hockey's Cabcharge account, details of which were hand written by the driver on the docket instead of being "embossed" with card details, had expired before the date of the trip.

The Senators and Members Handbook states that "the passenger should sign the contractor's travel docket, detailing the location, kilometres, time and cost of the trip and ensure these details are forwarded to Ministerial and Parliamentary Services".

In his letter, Mr Skelton invited Mr Hockey to speak directly to Cabcharge founder Reg Kermode about the matter, supplying his direct line.

Documents show Mr Kermode's mobile phone number was hand written on the letter received by Mr Hockey's office.

Mr Skelton, now chief executive of Cabcharge, told Fairfax Media that the matter was "resolved with the Department of Finance and Deregulation".

"To the best of our knowledge the parties involved were satisfied with the outcome and police involvement was not pursued," he said in a statement.

Mr Hockey says he has "no recollection of speaking with Reg Kermode or Cabcharge as I believed such action would be inappropriate".

"To ensure absolute probity, I insisted that all correspondence with Cabcharge should be through the Department of Finance," he said from Washington, where he is serving as Australia's ambassador to the United States.

Mr Kermode died in 2014.

The documents released under freedom of information laws reveal Mr Hockey was already well apprised of the "apparent fraud" against his card at the time of the 2012 Cabcharge letter.

Discussions between the department and his office as part of an audit of the Cabcharge dockets had been ongoing on for a year.

At the time, the opposition led by Tony Abbott was on the attack over the latest scandal in federal politics: allegations that then Speaker of the House of Representatives, Peter Slipper, had misused his Cabcharge entitlements by handing over blank but signed Cabcharge dockets for drivers to fill out.

The Sydney hire car company favoured by Mr Hockey, Ecotaxi, was owned and run by Russell Howarth, a self-described former British riot policeman who would later become the face of the campaign seeking to outlaw the Uber ride sharing service in NSW.

On April 26, nine days after the Cabcharge letter, Mr Howarth – who was in the middle of unrelated court action that would lead to his bankruptcy - signed a statutory declaration that was forwarded to the Finance Department by Mr Hockey's office.

In it Mr Howarth declares the trips under investigation were "undertaken when Mr Hockey was in the vehicle" and that Mr Hockey "was not aware of the invoicing arrangements, nor did he sign/authorise the Cabcharge dockets".

"I acknowledge I had been advised by Mr Hockey's office on previous occasions for the necessity to submit invoices in the manner as required," he declared.

However, Mr Howarth told Fairfax Media that there was an arrangement with Hockey's office, which – along with Cabcharge - was fully aware he was filling out the dockets and signing them on Mr Hockey's behalf.

"We had a copy of his card on file and we would just write the details in. We actually did offer to invoice them and not charge them on Cabcharge," he said.

"But politicians have to use Cabcharge."

Mr Howarth insisted that Hockey's trips "were all above board" and for official functions.

In early 2012, Mr Hockey did not give any hint of the investigation unfolding in the background before the September 2013 federal election.

In fact, days after his London speech Mr Hockey was in Sydney demanding Mr Slipper be stood down as Speaker.

Mr Hockey was reported on April 27 to have told Channel Seven that the "commonsense view" was that Slipper should stand down from "the most significant position in the Parliament" until he was cleared of allegations against him.

"I'm a member of Parliament, I have standards, this is not up to my standards," he said.

Emails released to Fairfax Media reveal the concerns first raised by the department in May 2011 about a cancelled Cabcharge card being used for trips charged to Mr Hockey's account.

"It is the same driver for all transactions," the email says.

"I'm not sure how long this has been going on but I have seen dockets, from the same driver, dating back to February 2010. There are also dockets for 2009, but with a different driver".

Mr Hockey was first approached over the misuse of Cabcharge dockets linked to his account on June 9, 2011.

An email to Mr Hockey from the entitlements manager at ministerial and parliamentary services advises his office has been included in a regular audit and "post-payment check" of Cabcharge costs incurred by MPs.

It says his office had been contacted to confirm the validity of fares charged against a cancelled Cabcharge card.

One Cabcharge docket appears to be dated April 18, 2011. It specifies the trip taken was from "residence" to "Ch 7 [Channel 7]" return and charges $190 at the rate of $95 per hour, including waiting time.

But official travel records suggest Mr Hockey was not in Sydney on the day in question but in the United Arab Emirates on shadow treasurer business between April 17 – 23.

Fairfax Media was unable to contact Mr Howarth about this discrepancy on Sunday.

A follow up letter on August 25 advises the finance department has received more unsigned dockets and counsels Mr Hockey that this is contrary to Cabcharge conditions of use.

"As the manual dockets are neither embossed with your Cabcharge details nor signed by you, there is a concern that your card details have been fraudulently used," it says.

Mr Hockey is asked to advise if the trips were in fact taken.

In September, records show Mr Hockey's office was queried about the dockets.

"I've just spoken to [redacted] in Mr Hockey's office, as he wasn't available," a record of the transcript says.

"She assured me that these trips have all been taken by Mr Hockey, who usually just doesn't have his wallet on him, so he jumps out of the cab and rushes off".

The caller records that she again asked for a formal response to the letters sent to Hockey. Finally, in October, Mr Hockey responds.

Apologising for the lateness of his reply, Mr Hockey explains: "There are many occasions when I do not carry my Cabcharge card on my person."

"There are also some occasions where equipment failure and my hectic schedule prevent the normal issue/authorisation of travel dockets".

He adds that the dockets "are valid and payment may be processed. These trips are taken under entitlements".

The next month a further eight non-compliant dockets were received.

In November Mr Hockey is advised that Mr Howarth has been paid $3650.90 following invoices sent to the department.

On April 27, 2012, 10 days after Cabcharge wrote to Mr Hockey advising it was planning to refer the matter to the AFP, his office sent Mr Howarth's statutory declaration to the Finance Department's entitlements branch.

In June, Mr Hockey advises the department they should pay an invoice submitted by Mr Howarth for trips to the value of $3816.45 during 2011.

Mr Hockey said in a statement to Fairfax Media that he used taxis and hire cars in Sydney as they were cheaper than Commonwealth cars and can travel in bus lanes.

He said the dispute was between Cabcharge, the Department of Finance and Mr Howarth.

"There has been a long history of dispute between Cabcharge and hire car companies, including Mr Howarth's Ecotaxi," he said.

"Knowing that I used taxis and hire cars at various times, the parties sought to embroil me in their dispute."

Mr Hockey said he ceased using Mr Howarth's services after the matter was resolved.

"Every paid receipt was matched with appropriate travel," he said.

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