The invention relates to an access unit for communicating with a further access unit to control access to a vehicle. The access unit comprises at least a first transmitter for transmitting a polling signal; and at least a first receiver for receiving an authentication signal from the further access unit in response to the polling signal. At least the first transmitter is a first ultra-wideband transmitter and at least the first receiver is a first ultra-wideband receiver. The invention also relates to a vehicle access system which is a combination of the access and further access units. The invention also relates to methods of operating a vehicle access system and a vehicle access unit.