Europe's leading safety testing organisation has identified a “critical safety failure” with the driver’s seat of the MG 3, prompting an urgent update for the supermini.

In Euro NCAP's frontal offset crash test (in which 40% of the car’s front end collides with a barrier), it found the 3’s seat latching mechanism failed, causing the driver’s seat to twist during the impact. 

This caused a more severe impact on the crash test dummy’s right leg than if the seat had remained in place, resulting in a "poor" score for protection of the driver's right femur.

Euro NCAP said it had never witnessed a failure of this kind in its 28 years of crash testing.

The organisation added that MG implemented changes to reinforce the latching mechanism in August.

Euro NCAP also found that the driver’s head could "bottom out" through the airbag in a crash, meaning it graded the 3’s head protection as only adequate.

MG has promised to tweak the airbag in October, Euro NCAP said. However, the seat and airbag changes won't be applied to 3s that have already been delivered to customers since the model's launch last year.

Euro NCAP said it has reported the faults to type-approval authorities so that they can decide whether to issue a recall.

Autocar has contacted MG Motor UK for comment.

Following the findings, Euro NCAP said it will implement changes to how it scores crash tests; it doesn't currently have a mechanism for penalising cars in the event of component failures, so the 3 still scored four stars out of five.

“This is an almost unheard-of occurrence, but one that Euro NCAP will address through changes to our protocols and scoring so we can reflect any failure,” said Aled Williams, programme director for Euro NCAP.