City of London Police published the findings of an internal review after the £10m trial of the millionaire jockey and five other people, including two Yorkshire riders and a businessman, collapsed at the end of last year.

Commander Patrick Rice, who led the review, admitted that a series of errors were made during the investigation, which was launched four years ago and was the biggest inquiry of its kind.

However, he stressed that an overhaul of the force's procedures was already being implemented to prevent such mistakes being repeated.

Mr Rice said: "This report is the result of several months of painstaking work by the review team. We have been thorough in our efforts to identify exactly what we could have done better – or differently.

"I am pleased to say that we got a lot of things right, including the overall direction and control of the investigation. However, we have also identified some areas where we need to tighten up our processes and modify our ways of working."

Following the collapse of the Old Bailey trial on December 7, serious questions were raised over the funding of the investigation. It emerged that the British Horseracing Authority (BHA), the sport's regulatory body which alerted the City of London Police to its suspicions, had received a formal request for funding from the force but turned it down.

The internal review has now recommended that City of London Police should develop a formal policy for funding investigations as well as officially recording decisions on the resourcing of major incidents.

The force led the inquiry into allegations that the jockeys deliberately lost races to ensure a betting cartel profited.

But Mr Justice Forbes, who presided over the two-month trial in London, said evidence by the prosecution's sole expert witness contained "significant limitations and shortcomings".

Australian racing steward Ray Murrihy had been called in to give evidence as he was independent of the British horse-racing world, but admitted it was "not incumbent" upon him to be versed in UK regulations.

The police review of its investigation also recommended the force should fully adopt national guidelines on identification and appointment of an expert witness. The London force is also due to put in place an official protocol for dealing with regulatory bodies, such as the British Horseracing Authority.

Immediately after the case against Fallon collapsed the six-times champion jockey's lawyers demanded an inquiry into the police's evidence.

The case unravelled after it became clear there was no evidence that Fallon or any of the other jockeys on trial had ever deliberately "stopped" a horse.

North Yorkshire jockeys Fergal Lynch and Darren Williams were also acquitted, along with professional gambler and alleged ringleader Miles Rodgers, 38, a businessman from Silkstone Common, Barnsley.

Lynch's older brother Shaun and barman Philip Sherkle were also cleared. However, after Fallon was acquitted it emerged that he had tested positive for a banned substance, thought to be cocaine, and he was given an 18-month worldwide ban from horseracing.

City of London Police said yesterday that disciplinary action had not been taken against any of the officers involved for the failings in the case.

Commissioner Mike Bowron said: "Most of the learning has already been put into practice.

"We will now be working to implement the remainder without delay and I will ask Commander Rice to review progress in six months' time."

The prosecution had alleged the six defendants plotted to stop 27 horses winning between December 2002 and August 2004. Concerns were raised by internet betting exchange Betfair with the then Jockey Club, which is now the BHA, before the case was passed to City of London Police in 2004.

Two further trials involving five other defendants were subsequently dismissed after the collapse of the Old Bailey case.