A recently established body called the Kenya Flower Council, made up of 17 flower growers employing over 20,000 people, mostly women, says that one of its aims is "to grow flowers in such a manner as to safeguard the environment". The council this week opened an office in London. Its 17 growers account for 60 per cent of Kenya's flower production, and over 90 per cent of exports to Britain.
Two of its largest members are Sulmac, a Unilever company, and Homegrown, supplier to Marks & Spencer, each employing around 5,000 people. Asda, Safeway, Sainsbury's and Tesco also sell Kenyan cut flowers.
Growers can join the flower council if they agree to abide by a "code of practice". This requires them to give their employees a six-day working week of 46 hours, 21 days paid holiday a year after a year's service and two months paid maternity leave for women. For African farm estates, such conditions are good. Mr Evans also claims that members pay "well above the government minimum salary".
The flower growers are obliged by the code to reduce inputs of chemicals and to ensure that pesticides are used safely. Workers spraying pesticide "must wear protective equipment", for example.
However, Kenya's farmers use around 300 tonnes a year of a highly toxic poison and ozone layer depleter called methyl bromide. This is used to kill weeds and pests in the soil, but it accounts for about 10 per cent of global ozone losses. Also, along with weeds and pests, it kills everything else in the soil, leaving it sterile. Large amounts of fertiliser then have to be applied to make anything grow.
Kenya has been using more than 5 per cent of its foreign earnings to import methyl bromide, most of which is used by its flower growers and producers of export crops. Mr Evans said that there were no effective substitutes for methyl bromide, but that his company, Homegrown, had substantially reduced its use and was seeking alternatives.
Ms Barbara Dinham, speaking for the environmental charity, The Pesticides Trust, said that there are substitutes, "some of which are being used successfully in flower production". Solarisation - laying plastic strips on the soil to trap the sun's heat - is used to control pests effectively in Egypt, Morocco, India and Pakistan, for example.
From the "ethical" perspective, there is also a question mark over whether horticulture can continue to expand in Kenya without intensifying conflicts over land and water. The country is already short of land for producing food. One of the main flower growing areas is around Lake Naivasha, where flowers grow on land that was previously ranch land and small farms. Conflicts have been reported between expanding horticultural schemes around the lake and Masai cattle owners, who claim the surrounding land is theirs.
Irrigation systems used by the flower industry make heavy demands on local water resources. A Dutch Ministry of Agriculture official has estimated that an extra 15cm of water is being extracted each year from Lake Naivasha by the flower growers. This inevitably means that less water is available for farmers producing food crops.
Liz Orton of Christian Aid, which is running an ethical trading campaign, welcomed the Kenyan flower growers' initiative but cautioned that the code of practice would need to be independently monitored - something Mr Evans said he would welcome. "It's a good code if it's implemented," said Ms Orton, although she felt there was room for improvement, especially on workers' social conditions. "The monitoring would need some kind of mechanism by which the experience of workers could be fed into the process."
A further issue for a large consortium flying the "ethical trading" flag is the effects on small shops. Mr Evans admitted that the big supermarkets were easing out local florists in Britain, but said the supermarkets were also doing a lot to encourage people to buy flowers.