Public sector buyers will not adopt ethical food standards without legislation to force them, a former minister has warned.

Former Labour minister Chris Mullin has called for legislation that will make schools, hospitals and local councils switch to free range eggs.

Environment minister Jim Fitzpatrick, responding during a Westminster Hall debate yesterday, said the government believed change should happen on a voluntary basis, pointing out that his own department's canteen had decided to use only free range eggs without any compulsion.

Mullin argued that "fine words and lofty sentiments are not enough" and called for mandatory health and sustainability standards for all public sector food.

A government commitment to purchasing only free range eggs would "improve animal welfare, support British farmers, and not increase costs", he said.

"That can be achieved only with mandatory standards, not by yet another voluntary initiative.

"It would command great public support and bring public sector food into line with the food that people generally consume at home."

Mullin pointed out that only around 40 local authorities had followed the example of Lancashire County Council who decided to stop buying caged-hen eggs last September.

His argument applied not just to eggs, but to any factory-farmed products, he said.

However, Fitzpatrick said the government wanted to "drive up standards by means of the carrot and the stick - through voluntary as well as legislative measures".

Caterers at the Department for Environment, Food and Rural Affairs had voluntarily switched to free-range eggs and UK-sourced meat, he said.

"No legislation compelled them to do that. I am talking about a private sector catering contractor that is making a judgment based on what it thinks the consumer wants," he argued.

"It believes that by doing what the consumer wants, it will sell more of its products, thus making its business more efficient."