ON this bustling, city centre street in Glasgow, KFC – where you can chose between a 6, 10 or 14 piece “bargain bucket” of chicken – is just a few doors down from Burger King. Next door is one of several convenience stores where large bags of big brand confectionery jostle for attention with 99p servings of colourful sweets and the fridge is stocked with energy and fizzy drinks, and chocolate milk. The pub on the corner has a two-for-one deal on burger and chips meals, and further down you can get a pizza for a fiver if you eat by 5pm.

Then there is the comfortingly familiar scent of chips, coated in lip-smackingly-satisfying salt and vinegar, piping hot and plentiful. So plentiful, in fact, that an average portion of chips alone (380g) will provide half of my daily calorie intake.

This was the finding of a new report by Obesity Action Scotland last week, in which researchers visited 30 Glasgow chippies and found portion sizes had increased by a whopping 80 per cent since 2002. The largest portion found (775g) provided three quarters of an adult's energy requirement.

The organisation is calling for regulation to control portion sizes, mandatory calorie labelling and half-sized portions to be offered.

The organisation is also fully aware that while chips – still the most commonly consumed take-away food in Scotland – make easy headlines, cutting down on deep fried potato is far from the only answer. As Scots now consume a quarter of our calories on food eaten out and about, it is also calling for definitive action to be taken to tackle the way the “out of home food environment” – everything from restaurants to petrol station shops and ice-cream vans – encourages us to overeat.

Because, says Lorraine Tulloch, programme lead for Obesity Action Scotland, it's getting serious. Two-thirds of the adult population in Scotland are overweight. Health experts predict that if nothing is done some 35 per cent of people in the UK will be clinically obese within 15 years, putting themselves at serious risk of heart disease, stroke and Type 2 diabetes.

This is nothing to do with blame and fat shame. "It's increasingly difficult not to become overweight because we live in an environment where we are encouraged to overeat,” says Tulloch. "We know that portion sizes have grown over time and there's no calorie information on menus so we're all operating blind. We use unhealthy food very often because it is available and convenient. The important message is not 'don't eat chips'. It's about understanding what that means when you do.”

Leaving the wards of Glasgow Royal Infirmary at the end of a busy day Professor Mike Lean, consultant physician and chair of Human Nutrition at Glasgow University, firmly believes people need to know what obesity really means. So far today he's seen one patient who has gone blind, and two who have lost a leg – one of them has developed abscesses in the only remaining one – due to diabetes complications.

While the exact causes are still not fully understood, being obese is believed to account for 80-85 per cent of the risk of developing Type 2 diabetes, while recent research suggests that obese people are up to 80 times more likely to develop it than those with a normal body weight.

It's not just chips, Coca-Cola and Mar bars, he says, it's the whole push on take-away food, offered everywhere from petrol stations to vans outside schools.

He's also concerned, but not surprised, by the portion sizes. Food, he notes, has become cheaper than ever to produce, so why not make your bottle of Coke bigger, and encourage people to chose to buy more for the same price?

"When we get bigger our appetite grows and our bodies send messages to our brains to ensure we don't get any smaller,” he explains. “We are a very clever species. Other animals can get fat, but they can't get as fat as a human.”

Food and drink retailing is worth almost £30 billion annually across the UK. “Our economy depends on people buying more and the government is determined that we need to push towards growth,” adds Lean. “That's the free market. And the only way we can now deal with it is to regulate."

Regulation is not a popular position. In May this year, during a meeting with Jamie Oliver, First Minister Nicola Sturgeon agreed to curb junk food promotions like two-for-one pizza deals. There was an outcry with accusations of "class snobbery" and hypocrisy.

But Lean makes no apologies for his view. "We've got a tax on alcohol, smoking is banned in public places and that does have a positive effect. We are never going to ban chips entirely but maybe we need to ban vending machines selling chocolate –we even have them in this hospital – and vans targetting children outside schools."

He shrugs off "nanny state" arguments. Is it nanny state when someone tells us we all need to drive on the left hand side of the road, or when we ban sulphurous fumes bellowing from chimneys, he asks?

As to the argument that the unhealthy choices are often cheap, he doesn't follow the logic. So, he points out, was asbestos insulation, but it was banned because it was hazardous to health. "We now have 3.5 million people in the UK with Type 2 diabetes. Are we just going to brush them under the carpet? They are not just dying young they are suffering sometimes ghastly consequences."

Professor Franco Sassi, chair in International Health Policy and Economics at Imperial College London agrees the well-documented, super-size portion trend is simple economics. The costs, he claims, have been reduced by technology. "It's had the same effect on food as it's had on all sorts of consumer goods."

Yet technology also has an effect on the make-up of food itself, with palm oil used because its cheap, despite the fact that healthier, and more environmentally friendly options would be better for all. Meanwhile sugar and salt are used to increase taste and make-up for lower quality ingredients.

"The food industry should have been regulated long ago," he says. Instead the government's failure to act has seen a "tidal wave" of chronic diseases. It's costing society dear in many ways. An estimated four per cent of the UK health budget is spent dealing with the health fall-out of obesity.

Annie Anderson, professor of Public Health Nutrition at University of Dundee, claims portion size is only one element of a complex picture that is quite simply killing us. "For me it comes down to a mantra about availability, price and marketing,” she says.

"The amount of money that chocolate companies put into marketing a single product is more than our total budget for health promotion for the whole year,” she says. “It's become completely normal to graze all day and you're almost deviant if you don't. You have to be a very strong person to go against the dominant culture and some people don't have the time or capacity to do that.”

Anderson claims most people become over-weight simply because they are not taking active steps to avoid it.

"We have been working on this issue for decades and whatever has been done in the past, it is not enough,” she says. “There has been an emphasis on education but that's only a single component – it won’t change behaviour on its own.”

Local authorities have an important part to play, she argues. Research shows the more deprived an area, the more outlets selling fast food, alcohol, and tobacco are clustered in it.

Fiona Crawford, a consultant in public health for NHS Greater Glasgow and Clyde and the Glasgow Centre for Population Health, agrees that better urban planning is needed. Several years back she was part of a team involved in researching the out-of-school lunch choices of Glasgow secondary school pupils – including those in deprived areas – which unsurprisingly found chips, pizza and sausage rolls were among the most popular options.

One meal from a local shop contained 80g of fat, the maximum recommended daily intake for an adult man. Later they asked the 14/15 year olds what they could do? "They came up with a range of very sensible suggestions from putting better shops into housing schemes to discouraging fast food outlets," she says.

But if teenagers could see the solutions why have politicians failed for years to act? "The commercial food companies are very powerful," says Crawford. "Think about how long it has taken to get a minimum price on alcohol in place. We need to applaud the Scottish Government for the work they have done on tobacco and alcohol but now a sugar tax is absolutely the right thing to do.”

The Scottish Government says it is committed to change, last month publishing a plan for a Healthier Future in Scotland with proposals for bans on junk food promotions. But many argue cultural change is also needed.

For Pete Ritchie, director of campaigning organisation Nourish, it's about creating a more holistically-informed set of policies that join up health and equality concerns with cultural and social ones. Along with the Scottish Food Coalition, Nourish is working towards a Good Food bill that will join up legislation on agriculture, planning, social security, and public health..

“It's not wrong to be saying we need to control portion size,” says Ritchie. “That's important. But we also need to work towards a better relationship with between us and our food. We need to work towards caring about ourselves enough to eat what we need.” And then, he says, we need to find ways of putting what we need within easy reach.

Are you obese?

First find you Body Mass Index (BMI) by dividing your weight in kilos by you height in metres, then divide the answer by your height again:

• 18.5 to 24.9 means you're a healthy weight

• 25 to 29.9 means you're overweight

• 30 to 39.9 means you're obese

• 40 or above means you're severely obese

Generally, men with a waist circumference of 94cm (37in) or more and women with a waist circumference of 80cm (about 31.5in) or more are more likely to develop obesity-related health problems.