Low oil pressure and noisy top end.

My car was driving ok until i stopped at the garage and when i went to start the car again it wouldnt start.the AA was called and they got the car started, they said it was a suspected starter motor.after driving the car home i noticed that the car was indicating low oil pressure and souded noisy from the top of the engine.the car has been serviced by citroen dealership and agents and has covered 49000miles it was due a service two days after this happened.
i have been told that the timing chain tensioner idler somtimes collapses and can cause knocking noise from the cams.after having the car checked it would appear that the sump oil has been restricted and may have caused further damage.Is this a common problem on these cars? The car has had the injectors lifted out and thre is quite a lot