It would appear the vehicle has gone into limp-home mode. This limits how much power the engine produces and how fast the vehicle will go as a means of protecting the engine and transmission from damage due to whatever the root cause is. Often a low coolant or oil level or high temperature will force the car into limp-home mode, but there are many other reasons for this to happen. You need to take the car to a workshop which will be able to scan the vehicle electronically and gain a better idea of what’s going on.

Don’t forget, either, that provided you car is less than five years old and has travelled less than 130,000km, it should still be covered by the LDV factory warranty.

As for the colour of the oil, diesel engines are notoriously filthy things and nearly always turn their oil black in a very short space of time. In fact, even when topping up with new oil, by the time it has reached the sump and appears on the dipstick, it’s already black.

Any time the engine revs up but the car doesn't go any faster, you're a fair chance to have an issue with either the automatic transmission or the clutch in a manual car.

If an automatic doesn't accelerate when you give it some throttle, our suspicions would be with either the torque converter, something inside the transmission itself or the unit is low on transmission fluid. If a manual car does the same thing, it's usually a poorly adjusted or worn out clutch that is slipping, allowing the engine to rev up, but not transfer that power to the wheels.

Your car would have come with a five-year/130,000km warranty, so if it hasn't exceeded that kilometre limit, it should still be under factory cover. So make sure LDV fixes it as per the warranty terms and conditions.