The connection between tropical rainforests and digestive biscuits may not be obvious. That's because most people are unaware that when they sit down for a cup of tea and a biscuit, they are probably consuming palm oil.

Palm oil is found in thousands of food products and is one of several oils that can be labelled "vegetable oil" on a list of ingredients. Most of the world's supply comes from South-east Asia where countries including Indonesia and Malaysia, keen to provide economic opportunity for their growing populations, are clearing thousands of acres of forest to make way for plantations.

But this need not be the case. When grown and processed sustainably, palm is an excellent and environmentally beneficial crop because it so high-yielding, requiring less land than other vegetable oils. The problem lies in tracing the origins of the oil we put in our food.

As much as a third comes from smallholders working on micro-plantations who take their crop to a local mill for processing. This crude palm oil is then sent to refineries, often in Europe, where it is mixed with other shipments. This makes it difficult for manufacturers to pinpoint where their supply has originated, in order to determine whether it has caused any virgin rainforest to be destroyed.

For some years, an organisation called the Roundtable on Sustainable Palm Oil (RSPO), which Sainsbury's helped found, has been working on a solution. Last year, the first certified sustainable palm oil arrived on the market. Sainsbury's immediately started using it in our fish fingers, before rolling it out to the rest of our frozen fish range. We now use sustainable palm oil in our own-brand soap and next month it will be introduced to our digestive and rich tea biscuits.

Other UK retailers and manufacturers have not been as quick. Sustainable palm oil is expensive as it requires separate storage, infrastructure and growing practices. If more firms started buying it, it would stimulate the market and prompt more producers to make the necessary investment. This would lead to better prices, an increase in production and a decrease in deforestation.

The palm oil industry supports some of the world's poorest communities, so companies have a responsibility to work with suppliers and growers to make it sustainable as quickly as possible. Improving growing practices could double production, while at the same time protecting rainforests; plenty of land with little biodiversity value could be used for oil palm.

Sainsbury's has been leading the way in this regard, from being the first retailer to buy RSPO oil, to becoming the first to label it as "palm oil", helping consumers to become more aware of its importance to the food industry.

As shoppers become more aware of the issue, they will demand sustainable palm oil. As a result, we will switch to a 100 per cent certified sustainable supply in all our own-brand products by 2014.

Justin King is chief executive of Sainsbury's