Where, owing to the presence of a vehicle on a road, an accident occurs within Greater London and it appears to the Secretary of State that the sole or a contributory cause of the accident was—
the nature or character of the road or of the road surface, or
a defect in the design or construction of the vehicle or in the materials used in the construction of the road or vehicle,
he may, if he thinks fit, cause an inquiry to be held into the cause of the accident.
In this section " road " includes a highway and a bridge carrying a highway and any lane, mews, footway, square, court, alley or passage whether a thoroughfare or not.