The decision to reverse Jeremy Clarkson's deal to record a voiceover for a Top Gear satnav went to the very top of the BBC when director-general Mark Thompson "intervened", according to a report published today.
The plan, which breached editorial policy and left Clarkson "in potential breach of his contract", was only discovered by BBC bosses when they read about it in a newspaper.
More than 50,000 devices had already been made and many delivered to shops by the time it was decided the deal with TomTom ran against policy which prevents the show's presenters endorsing motoring products.
The devices were still sold but BBC Worldwide - the corporation's commercial arm, which struck the deal - did not make any profit, with proceeds going instead to Children In Need.
Today's report by the BBC Trust's editorial standards committee (ESC) said BBC bosses discovered the deal after an article was published on September 4 and Mr Thompson pulled the plug less than four weeks later on September 29.
It said BBC Worldwide "failed to recognise" the potential conflict of interest and said there should have been "an immediate referral to BBC editorial policy".
The report found the breach of editorial guidelines was not "deliberate", but it could have "undermined" public trust in the BBC.
It stated: "There were potential conflicts of interest in the presenter of Top Gear being seen to endorse an individual car-related product."
It continues: "On one level the compliance process worked i.e. the editor-in-chief, as the ultimate arbiter, intervened so that the deal did not progress as proposed, but this could have been resolved much earlier if various referrals or different judgments had been made."
The motoring show is described in the report as "one of BBC Worldwide's most successful global brands" which is shown in almost 200 different countries and is backed by sales of books, toys, clothes and other products including toothbrushes and duvet sets.
A spokesman for BBC Worldwide said: "We have reviewed the process for referrals between ourselves and the BBC public service on such commercial matters, and have introduced new measures to ensure a repeat of this situation is avoided."
This is not the first time the show and Clarkson has run into trouble.
Earlier this year, the show's bosses rejected claims that its India special was insulting and last year the BBC ended up apologising to the Mexican ambassador after remarks made by its hosts.
More than 21,000 complaints were made to the BBC last year after Clarkson said striking workers "should be shot" during an appearance on The One Show.