Sex is the main driver behind the district’s population boom, according to the leader of Bradford Council.

There will be an estimated 44,400 extra people living in the district by 2021, according to a new report drawn up by officers at Bradford Council.

Yesterday, the Telegraph & Argus revealed the strain this is expected to put on the district’s public services.

While many people think of immigration as the main cause of population growth, this is not the case in Bradford, with more people leaving the district than arriving, the report has revealed.

A high birth rate, and an elderly population living longer, are adding more to the local headcount, although about a third of Bradford’s babies (32.4 per cent) are born to immigrant families.

When asked about the causes of the district’s population boom, Councillor David Green (Lab, Wibsey) said: “It’s sex. People are having more babies. Is immigration a factor over the period 2001 to 2011? Yes I believe it is one issue, but it’s not the only one and I think anybody who tries to make out it’s a clear-cut issue is in danger of over-simplifying it.

“Clearly there’s an issue about the growing birth rate and there’s some challenge created by immigration, but there’s also opportunities created by immigration.”

Net international migration brings about 1,500 extra people to the district each year, according to the Understanding Bradford District report.

But this is eclipsed by the number of people leaving the district to go and live elsewhere in the UK.

Each year about 17,500 people leave the district for other parts of the UK, while only 13,600 people move here from elsewhere in the UK.

This net loss is one of the biggest in the country.

And Coun Green thinks it is down to people leaving to find jobs elsewhere.

He said: “If you become unemployed in Bradford and you get a job somewhere else, you’re going to take it.”

He said students going to Bradford University and Bradford College tended to be local, so they could be having to move away once their courses had finished to find work.

Coun Glen Miller, leader of the Tory group, said he believed the people leaving the district were more often aged over 45.

He said often they had saved up enough money to move to the coast, or into the Dales.