A vaginal swab was left inside a patient following treatment at Darent Valley Hospital, it has been revealed.

The incident in October 2016 was one of four "never events" recorded in the year to November at the Dartford site. There was just one such event in the previous three-year period.

In the same month the wrong type of knee replacement was inserted during surgery. The recipient later fell over and damaged the joint further and the error was only discovered during that surgery.

Eight months later a patient’s ovaries were inadvertently removed during a hysterectomy. She had requested her ovaries be preserved.

Last August the fourth never event left a patient requiring further surgery after an incorrect component was inserted during a hip operation.

The four incidents – three of which occurred in the operating theatre – has led the hospital to commission an external review into operating practices.

Staff involved have also been interviewed to “rule out capability or conduct concerns”, while new training has been brought in.

Speaking at Dartford and Gravesham NHS Trust's latest board meeting medical director Dr Steve Fenlon said it was a concern to see so many in a short space of time but it was not possible to know why this had spiked over the last year.

He noted nationally there were more than 400 never events with no sign of a significant reduction “perhaps due to increased awareness and the increased number of interventional procedures”.

Non-executive director of the trust Steve Wilmshurst requested never event reports be submitted to the board on a more frequent basis.