Unilever is preparing for a major campaign to highlight its sustainability credentials to consumers.

The company is putting a supplier auditing system in place that will allow it to show that its produce is grown in a green and socially acceptable way.

"We're looking to tell the story about our brands so that anyone who buys them understands the values that underpin them," said David Pendlington, sustainable agriculture manager. Unilever would in time look at putting the new ethical message on some of its brands, he added.

A new software-based farm auditing system will allow Unilever to quantify suppliers' progress against its long-standing 11-point sustainability programme, called Growing for the Future. The Quickfire system from Muddy Boots runs on handheld computers, which can be used in the field.

"Until now, the audit system has generated a pile of paper that is hard to interrogate," explained Pendlington. "The software will allow us to capture the benefits of our programme and help suppliers work out where they are on that journey."

The software will be trialled with 400 Europe-based Unilever suppliers behind the Knorr and Bertolli brands, over the next three years, in turn working with thousands of farmers.

Though suppliers have to buy the software, the company wants its entire supply base to be covered. Unilever is presently in talks over financing.

Ahead of the roll-out, Unilever is extending the system to third-party suppliers. It has cost the company £13.5m to develop and requires growers to work towards goals such as improving soil fertility and supporting local communities.

The software also underpins Marks & Spencer's Field to Fork assurance scheme and is used by foodservice operator Compass.