1. A computer-implemented method of controlling a vehicle, comprising: receiving one or more instructions issued as speech; analyzing the speech using speech recognition software to provide a sequence of words and a word confidence measure for each word so recognized; analyzing the sequence of words to identify a semantic concept corresponding to an instruction based on the analysis, and a semantic confidence level for the semantic concept identified derived at least in part with reference to the word confidence measures of the words associated with the semantic concept; providing a spoken confirmation of the semantic concept so identified based on the semantic confidence level; and using the semantic concept so identified to provide a control input for the vehicle.