Sainsburys plans to become the most socially responsible supermarket brand, said chief executive Justin King this afternoon.

Speaking at the Think 07 conference, King said the food retailer's decision to stock only Fairtrade bananas at all of its 800 stores by the summer would add £4m to its buying costs, but it would help build a reputation of responsible behaviour.  

'My responsibility to shareholders is to build up the power of the Sainsbury's brand,' he said. 'They are not too worried about individual financial decisions so much as the overall bottom line.'

Last Friday Sainsburys gave away 6.5m reuseable carrier bags, known as 'Bags for Life', throughout its stores in place of the usual disposable bags. Normally it expects to sell just 3.5m of the reuseable bags in a year. King said last Friday's giveaway is expected to save around 100m disposable bags over the next 12 months.

Rising fuel prices were more likely to encourage businesses to save energy than government regulation, King said. Recent rises in oil prices had 'knocked a £75m hole in my profit and loss account.' 

Sainsbury's new Northampton depot, to open this summer, 'will be the most environmentally friendly depot ever', King said, with a combined heat-and-power plant helping to cut energy use by 50-60%.

Think 07 runs from 1-3 May at London's Excel centre. For details go to www.Think07.co.uk