Brighton and Bristol are among eight local areas of England where less than a third of the population describe themselves as Christian, according to the latest census data.
Leicester and Slough have a similarly low proportion, together with four London boroughs: Camden, Hackney, Redbridge and Tower Hamlets.
The figures provide a snapshot of religious belief across England and Wales on the day of the census, March 21 2021.
They show around two in three local authorities (218) saw fewer than 50% of people describing themselves as Christian, while in the remaining third (113) the proportion was 50% or higher.
Tower Hamlets has the lowest proportion, at just 22.3%.
Leicester has the second lowest figure (24.7%), followed by Redbridge (30.4%), Hackney (30.7%), Brighton & Hove (30.9%), Camden (31.4%), Slough (32.0%) and Bristol (32.2%).
Other areas below 40% include Birmingham (34.0%), Nottingham (34.7%), Cambridge (35.2%) and Manchester (36.2%).
The lowest proportion in Wales is 36.4% in Caerphilly, followed by Rhondda Cynon Taf (also 36.4%) and Blaenau Gwent (36.5%).
The same three areas of Wales have the highest proportion of people describing themselves as having no religion, with 56.7% in Caerphilly, 56.4% in Blaenau Gwent and 56.2% in Rhondda Cynon Taf.
Brighton & Hove has the highest proportion in England saying they have no religion, at 55.2%, followed by Norwich (53.5%) and Bristol (51.4%).
Tower Hamlets has the highest proportion in England and Wales describing themselves as Muslim (39.9%), followed by Blackburn with Darwen (35.0%) and Newham in London (34.8%).
The highest figures for people describing themselves as Hindu are in Harrow in London (25.8%), followed by Leicester (17.9%) and the London borough of Brent (15.6%).
Overall, 27.5 million people in England and Wales described themselves as Christian on the day of the 2021 census, or 46.2%.
This is down from 33.3 million (59.3%) a decade earlier and is the first time the proportion has dropped below a half.
At the same time, the percentage of people saying they had no religion has jumped from around a quarter in 2011 (25.2%, or 14.1 million) to over a third in 2021 (37.2%, or 22.2 million).
