Official warnings could be sent to the parents of obese children as young as five, the government confirmed today, as Scotland launched a scheme to give free healthy meals to all primary school children.

The Department of Health confirmed that it favoured sending out warning letters to parents in England and Wales as part of a ministerial pledge to "go further and faster in the fight against childhood obesity".

News of the plan emerged as a pilot scheme began in Scotland today, giving all children in Glasgow and West Dumbartonshire free healthy meals for the first three years of school.

Adam Ingram, the children's minister in Scotland, said the scheme would be rolled out across the country if the six-month project was a success.

Currently, children in England and Wales are weighed at the ages of five and 10, but their parents are informed of the results only if they request them.

Under the new plans, parents could be handed the results automatically.

A statement from the Department of Health said no firm decisions had been made, but said: "We have been clear that we need to work harder to cut the rising levels of obesity in children ... the weighing and measuring programme is an important element of this.

"We need to take this further and help parents to understand the importance of healthy weight for their families and support them to make lifestyle changes."

The department said the national weighing programme was "critical to combating the rising tide of obesity".

In Scotland, the free school meals idea will be extended to schools in East Ayrshire, Fife and the Borders over the next few weeks.

The aim is to increase take-up of free school meals from 65% to 85%. Menus include soup, fruit and yoghurt.

If the scheme is rolled out nationally, it would cost the Scottish Executive up to an estimated £46m.

Speaking to BBC Scotland, Mr Ingram said: "These children will get the chance to sit down and eat with friends every day to develop a taste for healthier foods together. We hope these good lifestyle habits will stay with them as they grow up."

A report last week by the government's Foresight thinktank warned that a majority of Britons would be obese by 2050 if current trends continued.

It predicted that in just over 40 years, 60% of men, 50% of women and a quarter of all children in the UK were likely to be clinically obese.

A mere 10% of men and 15% of women were expected to have a "healthy" weight in relation to their height.

The impact of associated health problems would cost Britain more than £45bn a year, it said.

Obesity is controversial defined by body mass index (BMI), a measurement calculated by dividing weight in kilograms by height in metres squared.

A person with a BMI of 30 or above is described as obese. People who are overweight have a BMI of 25-29.9, while a BMI of 18.5 to 24.9 is considered normal.

The system can be unreliable because some healthy people, including many of the England rugby team, would be classed as obese using this measure.

But using the measure, the prevalence of obesity has more than doubled in the UK in the last 25 years, and having an "overweight" BMI is now the norm.