A report on events blamed for the departure of a London trust chief executive has revealed managers were “misled” about the extent of accident and emergency target breaches.

Tara Donnelly left West Middlesex University Hospital trust in February after eight patients had waited more than 12 hours to be admitted. The trust failed to inform NHS London as quickly as it should have done, it said at the time.

A serious untoward incident report on the waits, which happened on 19 January, says: “On 18 January, the management response to escalating emergency pressures was insufficient due to management being misled on the true extent of emergency pressures facing the trust.

“The chief executive was not kept appraised by the site on the situation, nor was she informed of the breaches until after the event. Nor were NHS London informed of the occurrence of 12 hour breaches.”

Additionally, the extent of the problem was at first not realised by senior management, allegedly because staff failed to enter three breaches into a computer system.

The report says: “During the early stages of this investigation, a further three 12 hour breaches which also occurred on 19 January were identified and formally reported to NHS London on Friday 23 January 2009, thus totalling eight breaches.

“The breaches were not identified immediately due to alleged falsification of data on the trust A&E system.”

A spokesman for West Middlesex told the Hounslow Chronicle, which revealed contents of the report: “The trust confirms that the investigation found that the altering of computer data in relation to 12-hour trolley wait reaches, as referred to in the report, was an isolated incident and that there was no evidence that data has been changed in the past.”

He declined to comment further.