text: Jerome Lavrilleux said the former president was not aware of the "slip".
  It comes after a lawyer for an event organiser accused the UMP of ordering almost 11m euros ($15m; Â£9m) worth of fake invoices to cover overspends.
  Reports say the scandal could damage the party and complicate any efforts by Mr Sarkozy to be re-elected.
  Police searched the headquarters of the UMP in Paris on Monday afternoon.
  "There have been anomalies," Mr Lavrilleux, a deputy director of Mr Sarkozy's 2012 presidential campaign, told France's BFM TV. with tears in his eyes.
  "There was no wrongdoing, there was a terrible spiral, a train going at high speed and people who should have pulled the emergency alarm and didn't, and I was probably one of them," he said.
  He said Mr Sarkozy, UMP Chairman Jean-Francois Cope and Batien Millot, the founder of the events company Bygmalion, were not aware of the actions taken.
  It comes after Patrick Maisonneuve, the lawyer for Bygmalion, told the same television station that the centre-right UMP had ordered fake invoices to cover exploding campaign costs.
  He said it was made clear to Bygmalion that if it did not comply, it would not be paid.
  The UMP's chairman was already facing growing speculation that he will have to step down after the French newspaper Liberation reported this month that the party paid some 20m euros to a unit of Bygmalion, founded by two associates of Mr Cope, to organise campaign events.
  Mr Cope told BMF TV earlier on Monday that he knew nothing of any wrongdoing.
  He said he had put his trust in the people who were responsible for the party's accounts and did not think he had to look over their shoulders.
  Mr Cope was already expected to face challenges for the leadership of the party after the UMP's poor result in the European Parliament elections. It came second to the far-right Front National.
  Mr Sarkozy, who lost the presidency to Francois Hollande in 2012, is rumoured to be preparing to make a comeback in 2017.
  He has not commented on the scandal over his 2012 campaign finances.
target: A senior member of France's opposition UMP party has admitted there were "anomalies" in the accounts of Nicolas Sarkozy's 2012 presidential campaign.