Leading article: Take a close look at the produce on offer

Marks & Spencer has become the latest major company to flaunt its environmental credentials. Its chief executive, Stuart Rose, has unveiled a grandiose "eco-plan" that pledges to "set new standards in ethical trading". We are told M&S will cut energy consumption, increase use of renewable power and convert its lorry fleet to bio-diesel. It also pledges to source more food from the UK to reduce the amount of produce flown in. On waste, M&S promises to send no more refuse to land-fill and to ensure all of its products and packaging are recyclable by 2012. On the production side, its polyester clothing will be made from recycled plastic bottles instead of oil.

This follows a flurry of similar initiatives by the large supermarket chains last year. Sainsbury's is developing biodegradable packaging, while Tesco is converting three-quarters of its transport fleet to bio-fuel and introducing incentives for its customers to reuse their plastic bags. M&S is going further than both.

So what is going on here? Have the executives of these retailers, after years of indifference, suddenly become green activists? Up to a point. The M&S plan is projected to cost £200m over five years. That is less than 0.5 per cent of its annual turnover. Yet the company is likely to spend a huge amount promoting its new "ethical" stance. That suggests managers such as Mr Rose believe the new stance will attract more customers. Investing in environmental projects increasingly seems a sound business strategy. That is by no means a bad thing. This "green" bidding war between the food retailers is a sign of the growing clout of environmentally conscious shoppers.

But it is beholden on ethical consumers to scrutinise carefully the details of such plans and, most importantly, check on delivery. If any company expects to reap the benefits of a green tinge, it must not be allowed to get away with mere spin.

Take packaging. The amount of packaging used by food retailers is a disgrace - and M&S has a particularly poor record. It must demonstrate real improvements in this respect if it is to make claims of ethical retailing. It is not enough to make packaging recyclable - M&S, like its competitors, should use less in the first place. We will be equally sceptical of promises to reduce "food miles" on produce. There should, of course, be taxes on aviation to deter retailers from flying in large amounts of unseasonal produce from abroad. Until then, we need to see genuine evidence that retailers are putting the climate before profitability before they can win any environmental plaudits.

Another cause of concern lies in the language. Mr Rose claims M&S will be "carbon neutral" in five years by using cleaner energy and carbon offsetting. But what does this really mean? In truth, we should be wary of this term, which is in vogue but all too vague. Supporting forestry schemes and energy-efficiency programmes through corporate donations is something to be welcomed, but such donations cannot be truly said to "offset" pollution. No large commercial organisation can accurately be described as "carbon neutral".

It is good news that leading firms such as the broadcaster BSkyB and the banking behemoth HSBC are taking serious steps to reduce their impact on the environment. And it is especially pleasing to see supermarkets, with their formidable carbon footprints, showing an interest. After all, M&S alone is responsible for 2,000 factories, 10,000 farms, 250,000 workers and 500 stores. The potential here for protecting the environment is enormous. But it is deeds, not words, that matter. And there is a long distance to go before we can hang out the bunting to celebrate the advent of a truly "green" high street.