He admitted that in order to hit its target of doubling the amount of UK-sourced food "we will have to make some big decisions to raise that figure above the 60-70 per cent we're currently heading for".
But he went on: "When we set those targets, we didn't know how we would achieve them, and we probably won't achieve them all - they are very challenging. But you can't sit on your hands waiting until you have enough data to make a business case - you have to place your bets based on your beliefs."
The retailer looks for such values in its suppliers too, he said. "Shared values give rise to the best kind of business relationship. You can't be successful working with or for Sainsbury's unless you share those values."
He described suppliers as "pivotal" to the company's success. "That's why we have this event," he explained. "Half our sales are own-label, so they have to be different both from other retailers' own-label lines and from branded goods."
The retailer is the only one of the big four supermarkets to have gained market share over the past year, with a "spike" seen during the horsemeat scandal, he added. "In a downturn, consumers don't abandon their values, they become more concerned about how they spend what they have. Some 84 per cent say how and where food is produced is important."
British Growers chief executive James Hallett said: "Sainsbury's is leading the way in its commitment to British farming. Other retailers are aware of it and following their lead to ensure their supply chains are resilient and able to deliver for the long term."
Inside track on securing the right partner for retailing
Clive Goatham, senior partner, AC Goatham & Son
"It was hard for us to find a partner that shared our values but Sainsbury's had a proactive top-fruit team who would join growers on farm walks - it's unusual for retailers to do much outside working hours. That helped us make the judgement call on the people we would have day-to-day relationships with.
"Sainsbury's has been instrumental in the rejuvenation not only of top fruit but of UK farming. However, you have done little through the media to tell this story. You should tell the nation about what you achieve."