All modern diesel vehicles will include a Diesel Particulate Filter.
The Filter holds a limited amount of soot (created during the combustion process) that needs to be cleared via a process called regeneration to ensure the vehicle runs properly.
Regeneration occurs when the vehicle is driven at a fast enough speed to achieve a suitable temperature of exhaust gas. Typically a vehicle must be driven at 50mph for at least 20 minutes.
If the vehicle is not driven in this manner an excess of soot will build up. A warning light will inform you, however if ignored can cause damage to the vehicle.
If you plan to use the vehicle for town-based, slower journeys it may be worth considering petrol vehicles or alternatively taking the vehicle on longer journeys to ensure the vehicles reliability.