ore than one in 10 flats, terraces and semi-detached homes in some areas of England are officially considered overcrowded, with the proportion rising to at least one in five in parts of London, new figures show.
There are also sharp contrasts in levels of overcrowding across different religious and ethnic groups, which may reflect differences in age and background among households.
The data is the latest to be released from the census, which took place in England and Wales on March 21 2021.
It shows the proportion of flats considered overcrowded was highest in the London boroughs of Barking & Dagenham (22.7%), Newham (21.8%) and Redbridge (20.0%), along with Slough in Berkshire (20.8%).
There were 38 local authorities where at least one in 10 flats met the criteria for being overcrowded on the day of the census, 28 of which were in the capital and all in south-east England, except for Leicester (16.0%).
London boroughs also came first for overcrowding in terraced housing, with Newham (18.6%) and Barking & Dagenham (13.6%) recording the highest proportions.
But there is a greater spread of geographical areas at the top of this list, including Leicester (13.2%), Birmingham (11.9%), Oldham (10.6%) and Manchester (9.4%).
A household is classed as being overcrowded if it has fewer bedrooms than required, according to the Office for National Statistics (ONS) which published the data.
To determine if a household has enough bedrooms, residents are divided into types, each of which should have their own room – for example, an adult couple, any other adult aged 21 or over, two males aged 10 to 20 (sharing), two females aged 10 to 20 (sharing) or two children aged nine and under.
Overcrowding in semi-detached properties at the time of the 2021 census was again highest in London, affecting more than one in four households in Newham (26.2%), followed by the nearby boroughs of Tower Hamlets (19.7%) and Barking & Dagenham (17.9%).
Outside London, the highest figures were for Slough (14.9%), Luton (10.7%) and Leicester (10.4%).
The pattern is similar for overcrowding in detached homes, with Newham once more topping the list (26.3%), followed by Tower Hamlets (21.8%) and Barking & Dagenham (21.3%), while Manchester (11.5%) and Slough (11.1%) are highest outside the capital.
The local authorities that saw the lowest levels of overcrowding tend to be largely rural areas or parts of the country with few built-up areas.
Allerdale in Cumbria recorded the lowest rates for flats (0.8% overcrowded) and the Derbyshire Dales was lowest for terraces (1.2%), while Craven in North Yorkshire had the lowest rate for semi-detached properties (0.9%) and Rutland in the East Midlands was lowest for detached homes (0.3%).
There are sharp differences in levels of overcrowding when looking at other characteristics, such as religion and ethnicity.
Some 22.5% of households in England where all members identified as Muslim were classed as overcrowded – more than five times more likely than all households (4.4%).
For other religions the figure is even lower, at 3.0% for Christian-only households and 2.8% for Jewish, with 8.8% for Sikh and 9.1% for Hindu-only homes.
The figures may reflect the different age profiles of religious groups, the ONS said.
The average age of people in England and Wales identifying as Muslim at the time of the census was 27, while for people identifying as Christian it was 51.
Among ethnic groups, households in England where all members identified as black had the highest level of overcrowding (16.1%), followed by those that were Asian-only (14.6%) – well above the equivalent figures for mixed (6.5%) and white (2.5%).
For households with two ethnic groups the figure was 11.1%, while for three or more ethnic groups it was 12.1%.