The company says it has responded following parts shortages that affected several manufacturers during last year.
XPart, a sister company of MG Rover, has agreed that if a customer's car is off the road and needs parts, the MG Rover dealer or authorised repairer will quote a completion time.
If the deadline is not met through the late arrival of parts, then a special Parts Pledge programme will fund courtesy car costs until three days after the parts are delivered. John Parkinson, managing director of XPart, said: 'We experienced parts shortages in 2002. This led to a major review of the parts process and, where appropriate, fundamental changes were made.
'Parts availability for new MG and Rover cars has now reached 95% and will continue to improve. This gives us the confidence to operate such a ground-breaking initiative.
'A key business objective is to offer our customers an exceptional aftersales service. This programme will provide customers with added confidence and signals a much improved parts situation with excellent availability on current MG and Rover car ranges.'
Last year, Fleet NewsNet revealed that the Association of Car Fleet Operators had launched an initiative to reduce the number of occasions when cars are off the road due to a lack of spare parts following an accident or mechanical failure. The move won support from more than 20 manufacturers who agreed to take steps to end the problem.