This is the Car or Van Availability data (KS404) from the 2011 Census. The data provides the number of cars in households.
The question was:
In total, how many cars or vans are owned, or available for use, by members of this household? Include any company car(s) or van(s) available for private use
4 or more, write in number
The 2011 census in England and Wales took place on 27th March 2011. It provides a snapshot of the population and its characteristics on that day.
Further information about the census estimates, including details about the methodology is available here: http://www.ons.gov.uk/ons/guide-method/census/2011/index.html
Cars or vans
The number of cars or vans that are owned, or available for use, by one or more members of a household. This includes company cars and vans that are available for private use. It does not include motorbikes or scooters, or any cars or vans belonging to visitors.
The count of cars or vans in an area relates only to households. Cars or vans used by residents of communal establishments are not counted.
Households with 10 or more cars or vans are counted as having only 10.
Responses indicating a number of cars or vans greater than 20 were treated as invalid and a value was imputed.
A household is defined as one person living alone, or a group of people (not necessarily related) living at the same address who share cooking facilities and share a living room or sitting room or dining area. A household must contain at least one person whose place of usual residence is at the address. A group of short-term residents living together is not classified as a household, and neither is a group of people at an address where only visitors are staying.