The Guardian, in conjunction with Generation Rent, has found that Birmingham, Edinburgh, Bristol and all of south-east England rank among areas where young couples could be financially hindered from having children because they are paying too big a share of their income to their landlord.

Using the average regional full-time wage for workers in their 20s and 30s and the cost of privately renting a two-bed home in the area, the research found that young couples would have to spend more than 30 per cent of one full-time earner’s wage to keep a roof over their head in 66 per cent of the country.

There is no official definition of what a family can afford in the UK, but housing charity Shelter says it amounts to 33 per cent of income, while the National Housing Federation says it is 25 per cent. In the US, the Department of Housing says the baseline is 30 per cent; if rent is above this level, families “may have difficulty affording necessities such as food, clothing, transportation and medical care”.

The findings have renewed calls from housing campaigners for rent caps to be reintroduced after being abandoned more than 20 years ago.

The only areas that remain affordable are in the north-west, north-east and Yorkshire and the Humber. Northern Ireland was also affordable when measured against the average income for all age groups. There are no separate figures for young workers in the region.

The most inaccessible place for those wanting to start a family was London, with a two-bedroom rental there costing 60 per cent of the average income for someone in their 20s and 44 per cent for someone in their 30s. This was followed by the south-east, south-west and the east of England.

Betsy Dillner, director of Generation Rent, said: “For people on modest incomes, having a child will normally involve one parent staying at home while the other works full time, for a period longer than parental leave normally covers. That means a typical new family will rely on one full-time salary to make ends meet. If the rent is too high, that makes the arrangement unviable.”

For those on lower incomes, Dilner said: “The situation is even worse, with constant anxiety over how to put food on the table, and nothing left at the end of the month to put aside for the future.

“Not only do young adults face renting for a longer period at a higher cost than their parents, and may never actually buy a home, they are less likely to start a family – a prospect that ought to terrify older generations and policymakers alike.”

She added that if local leaders did not want to see their communities decimated by the housing crisis, they needed to start building on the “uglier parts of the green belt” and introduce rent controls.

In the Guardian’s study, Wales ranked as one of the more affordable places to start a family while renting. In 2015, the average annual rent for a two-bedroom home took 31 per cent of one full-time worker’s wage in their 20s, above the level of affordability. For someone in their 30s, it was 23 per cent.