Details of extra people were added to the 2001 Census to make it more complete, the head of the Office of National Statistics has admitted.

It follows a story first reported in The Guardian newspaper that officials had "made up" the details of residents including where they lived, their age, occupation, income and children.

The census had an 98% response and Len Cook, registrar general of the Office of National Statistics, said they had used "standard sampling techniques" to redress the balance.

Pre-school children - one group who were under represented

"It would be absolutely wrong to use the term 'made up'," Mr Cook told BBC Radio 4's Today programme.

"We used sampling methods which are quite orthodox."

He likened it to giving a representative total temperature for the UK based on samples from different points.

The statistics office used a sample of 320,000 people to build up a picture of certain parts of society it had had difficulty getting a response from.

Left out

According to the Guardian, these included women aged 85-plus, men in their twenties, pre-school children, non-English speakers and people living in privately rented flats.

Mr Cook said some households had been difficult to get to, particularly in inner cities, and some people had been unwilling to fill in the forms.

The sampling provided the statisticians with a "rich amount of detail" on people "who should have been in the census but didn't complete forms" said Mr Cook.

The first statistics from the 2001 Census are due to be published next week.