Caterers must serve fish a certain number of times per month or week – depending on whether they serve lunch only or lunch and dinner – and will  have to cook vegetables and pasta or rice in unsalted water.

From September 2011, all new catering contracts will have to comply with the standards, developed by the environment and health departments.

The standards include a mandatory minimum level – for example that at least 50 per cent of desserts offered are based on fruit – and a voluntary best practice level – for example that all sweet snacks are only served in the smallest portion size available.

Public health minister Anne Milton said: "The standards show that government is leading by example – by making sure there are healthier choices for people and that people have the right information at hand so they can choose healthier food more easily."

The standards also include sections on sustainability and animal welfare. All food bought by government departments will have to meet British or equivalent standards of production, as long as this can be achieved without increasing overall costs. All fish should be sustainably sourced, and catering equipment will have to meet certain energy efficiency standards.

Standards for other products and services – such as ICT, transport, paper and furniture – have also been revised to ensure they represent value for money while reducing environmental impacts.

More details on the food specifications can be found here: http://sd.defra.gov.uk/advice/public/buying/products/food/