Adverts for food which is high in fat, sugar and salt should not be broadcast before the 9pm watershed, according to the public health minister for Scotland.

Michael Matheson has written to Westminster Health Secretary Andrew Lansley to ask whether he would support a move to introduce a ban across the UK.

It follows recent research from Newcastle University which suggests children are still being exposed to the same levels of advertising for such foods, despite Ofcom banning these commercials during programmes aimed at youngsters.

Mr Matheson said: "Broadcast advertising influences the choices made by children and can shape their attitudes to food as they grow into adulthood.

"Tackling obesity and encouraging people to make healthier life choices is one of the most important things we can do to improve the health of our nation.

"The reality is that broadcast advertising is delivered across the UK and we need strong action and co-operation between governments to address this issue.

"According to the UN and Ofcom studies, the restrictions brought in by Ofcom have been adhered to by children's channels and broadcasters showing programmes specifically aimed at children.

"However, a loophole exists that allows HFSS (high in fat, sugar and salt) food adverts to feature during programmes with a high child audience such as soaps and talent shows.

"That's why we want to introduce a pre-watershed ban and are looking to the UK Government to support such a move which would carry the additional benefit of encouraging our partners in the food industry to reformulate their produce to lower salt, fat and sugar content."

Jane Landon, deputy chief executive of the National Heart Forum, said: "We welcome the public health minister's call on the UK Government to restrict unhealthy food advertising before 9pm. The existing rules have delivered protections in principle but not in practice.

"The current crisis in children's dietary health urgently demands bolder measures.

"Moving up to a 'watershed' restriction will help achieve the original policy aim to 'reduce substantially' children's exposure to advertising for foods high in fat, sugar and salt."

Dr Sally Winning, deputy chairman of BMA Scotland, said: "The role of advertising cannot be underplayed in relation to its impact on children's behaviour.

"BMA Scotland is concerned that children receive a huge amount of attention from food advertisers, with a marked discrepancy between the foods marketed at children and the nutritional quality of that food.

"The media has an important role to play in forming attitudes to nutrition and there is scope to harness this potential and further regulate its more harmful impact.

"Whilst the advertising of unhealthy foodstuffs, including inappropriate sponsorship of programmes and events targeted at school children is already regulated, it should be noted that many of the TV programmes most watched by children are not children's programmes, and so further consideration must be given to addressing this."

A Department for Culture, Media and Sport spokesman said: "The Government continues to keep this area under review and recognises that there are calls for increased restrictions on HFSS food and drink advertising.

"However, it is widely accepted that advertising has a modest, direct effect on children's food choices and is just one aspect in determining children's choice of food.

"It is also recognised that advertising can play a positive role in promoting healthier choices.

"The Government believes the current rules are a proportionate and balanced contribution to the wider range of measures aimed at tackling childhood obesity and poor diet.

"The Government is taking action, including through Change4Life and the Responsibility Deal, to ensure children get the best start possible in life and to make it easier for families to make healthier choices and follow a balanced diet."