Allison Vitalis is using vouchers to buy oranges, apples and plums at her local market in east London. Last week, she exchanged her vouchers, each worth £1, for cassava, plantain and yellow yam at the neighbouring Caribbean stall.

“As a single mum living on benefits, since I took the decision to stay at home to bring up my three-year-old daughter, Ariette, it’s been a struggle sometimes finding the money for fruit and vegetables to feed the family,” she says. “So the vouchers are really beneficial.”

Vitalis is one of 80 families and pregnant women on low incomes to take part in a pilot voucher scheme in children’s centres in two London boroughs, Hackney and Greenwich, that successfully increased the intake of fruit and vegetable in both children and adults and is now being rolled out across the capital.

“Research shows that what you eat in your first three years helps to define your physical shape, your intellectual capacity and life changes. Yet for families on low incomes it’s difficult to prioritise eating a nutritious diet,” says Mike Morris, chair of Alexandra Rose Charities, which is behind the scheme.

The government’s 2010 white paper Healthy Lives, Healthy People acknowledges that children’s diet “is crucial for their future health and wellbeing”. Since 2006, its means-tested NHS Healthy Start programme has provided vouchers for milk and fresh and frozen fruit and vegetables to eligible pregnant women and families with children under four (those on low incomes who qualify for income support, jobseeker’s allowance, employment and support allowance or child tax credits). According to Department of Health figures, in 2012 around 600,000 women and children in more than 450,000 low-income families in the UK were in receipt of these statutory food subsidies. An evaluation of Healthy Start, published last month, found that families on vouchers expanded the range and quantity of fruit and vegetables in their diet.

But there are concerns about the ongoing effectiveness of the NHS programme. Alison McFadden, senior research fellow in the school of nursing and midwifery at Dundee University and lead author of the recent evaluation of Healthy Start, explains: “While families greatly value the vouchers, their value is depreciating as the cost of fruit and vegetables rise and families report a lack of access in some areas to registered retailers.”

Working with local children’s centres, the Rose vouchers scheme identifies families eligible for Healthy Start and gives them weekly vouchers on top of Healthy Start money to spend at local fruit and vegetable markets. Pregnant women receive Rose vouchers worth £3 a week, while families get vouchers worth £3 for each child aged between one and four and £6 for each child under one, which can only be redeemed for fruit and vegetables on participating stalls. Stall holders claim back the value of the vouchers from the weekly rent charged for their pitch.

Managed by Brighton-based Food Matters, the schemeis based on a US model that doubles the value of federal nutrition benefits if they are spent at local farmers’ markets. By targeting local markets, Rose vouchers are designed to enable families to buy a larger quantity of healthy food from somewhere they can easily get to and that has more choice. “The markets are much cheaper than the supermarket and, as a Caribbean family, we can’t get a lot of the food we enjoy in the supermarket,” says Vitalis.

Not surprisingly there is some overlap between food bank users and Rose voucher recipients. Vitalis says she had to go to a food bank on a couple of occasions when paying bills took priority over money for food. But Morris says Rose vouchers are about helping people eat more healthily, not preventing hunger. “The charity is aware of the food bank movement but this is about good nourishment, not about providing a lifeline,” he says.

The scheme couldn’t be more timely. Earlier this week, a Fabian commission on food and poverty reported that a squeeze on incomes and a rising cost of living means that poorer families in the UK are trading down towards diets that are higher in fat, salt and sugar.

With fruit and vegetables costing approximately three times more per calorie than less healthy foods, it heard evidence from families who never eat them. “When you only have £19 for food each week, you end up with crap stuff,” one person told the panel. “I’d always look at how much it is going to fill you up,” said another explaining how she decides what food to buy.

Growing food poverty also increases health inequalities. People on lower incomes are one and half times more likely to get diabetes than those on higher incomes and to have a lower life expectancy. And the Cabinet Office predicts that 70,000 deaths could be avoided each year if UK diets matched nutritional guidelines on fresh fruit and vegetables. The UK government spends millions on public health campaigns such as 5 A Day and Change 4 Life, but if low-income families can’t afford to buy healthy food it would be better diverting some of that cash to subsidise the cost of purchasing more fruit and vegetables, suggests Jonathan Pauling, chief executive of Alexandra Rose Charities. “If you’re on a tight budget, do you think I’ll try this broccoli, which my two-year-old may or may not turn her nose up at, or do I buy this frozen pizza which doesn’t go off and the kids will definitely eat. You can’t take the risk,” he says.

Since the pilot ended in September, Hackney council has paid £6,300 for 75 families – a fraction of the 3,500 eligible for Healthy Start vouchers in the borough – to receive the vouchers and is exploring whether it could be extended. “As well as the health benefits these vouchers provide, they’re also a great way to get people using our local markets and supporting market traders,” says Feryal Demirci, Hackney’s cabinet member for neighbourhoods.

Across the capital, at Brixton market, traders will soon be accepting Rose vouchers distributed through six children’s centres in Lambeth to an initial 80 families as part of a scheme funded by the Greater London Authority.

Pauling hopes to raise £500,000 from charitable foundations to roll out Rose vouchers to more low-income families across the UK. “The vouchers could be applicable to any urban area in Britain,” he says. “Our goal is to work with any local authority that wants to work with us at a time when food poverty is on the rise.”