The biggest police tax probe into Premier League corruption has been beset with problems from the start.

Rumours of corrupt dealings, bungs and bribes have dogged those at the heart of our national game for years.

Since Brian Clough and George Graham were linked with backhanders in the 1990s, a string of high-profile names have had their reputations called into question.

But despite at least nine arrests, there has not been a single conviction.

It is five years since City of London police launched an initially low-key inquiry targeting alleged financial corruption in the multibillion-pound-a-year industry.

Detectives from the economic crime unit at City of London Police were assisted by HMRC inspectors as they scoured the private dealings of the sport's mega-rich for evidence of corrupt cash changing hands.

Police insisted their investigation was independent of an inquiry commissioned by the Premier League.

In 2006, the football body brought in former Metropolitan Police Commissioner Lord Stevens and his company Quest to examine several hundred transfers.

But it is clear the police and Quest investigators may have several common areas of interest.

The paper trail which led officers to Harry Redknapp stemmed from an interview he had given to Quest.

The Quest inquiry was set up by Premier League chief executive Richard Scudamore following allegations by Sven-Goran Eriksson.

Eriksson was caught making several indiscreet comments referring to murky financial dealings by an undercover reporter.

Luton Town manager Mike Newell also thrust the issue into the spotlight when he told BBC's Panorama that agents tried to pay him money for illicit transfers.

The Quest team said five football clubs - Chelsea, Newcastle, Bolton, Middlesbrough and Portsmouth - would face further investigation into their transfer deals.

However none of the five clubs, who all co-operated with the inquiry, were reported for breaching transfer regulations.

The inquiry raised concern about 15 agents and third parties involved in 17 transfers.

Some included household names such as Chelsea stars Didier Drogba, Petr Cech and Michael Essien.

Suspicions about one of those transfers were deemed to be sufficiently serious to be referred directly to the police and were not published in the report.

Meanwhile responsibility for the remaining 16 "uncleared" transfers was returned to the Football Association.

Officials at the FA and football's world governing body Fifa have examined the evidence provided by Lord Stevens.

Sports minister Richard Caborn said he was "deeply concerned" that some agents did not co-operate with the Quest team, while Redknapp told Southwark Crown Court that many other managers had not co-operated to the extent he did.

Lord Stevens has since said anti-corruption legislation was inadequate.

He said: "Those of us who have been at the sharp end of investigating corruption have found it is exceedingly difficult, on occasions, to get to the truth of the matter.

"Complex laws don't allow you to drill down into the real substance and gain the evidence you need to convict people for the type of corruption we're talking about.

"I think the current laws regarding bribery and corruption have been adequately described as 'obscure, complex, inconsistent and insufficiently comprehensive'.

"Surely that situation cannot be allowed to continue."

The City of London Police's Operation Apprentice has been running since the end of 2006.

Sources claim there has been a tense relationship between detectives and tax inspectors after the HMRC were drafted in to help.

David Gold, the former Birmingham City chairman now at West Ham United, described the affair as "a witch-hunt against football".

"I don't know why it has taken so long," he said.

"These people have lives to live. It is not fair. They should be respected, not treated like criminals."

Under the guidance of Detective Inspector David Manley, Apprentice investigations focused on the activities at Portsmouth between November 2007 and April 2008, leading to the eventual arrest of then Portsmouth manager Redknapp, former Portsmouth chairman Milan Mandaric and the club's chief executive, Peter Storrie.

The operation did not want for manpower, with around 30 officers raiding Redknapp's home at dawn.

But the drawn-out nature of the investigation caused resentment among those involved.

That anger will not be going away fast after the £8million inquiry boiled down to nothing.