Thirty years ago, hippos and Maasai cattle herders shared the shoreline of Lake Naivasha in the Rift Valley of Kenya with the small local community of farmers and fishermen. The lake was judged one of the 10 top sites for birds in the world; its acacia and euphorbia trees were famed for their beauty; and its clear, fresh waters were abundant with fish. The human census in 1969 showed just 27,000 people living in the surrounding areas.

The British and Kenyan governments weighed into the growing debate over "food miles" yesterday, insisting it was ethically and environmentally sound to buy flowers from Kenya on Valentine's Day.

There is increasing concern at the amount of carbon emitted by the fleets of aircraft that carry millions of flowers to Europe every day from the impoverished east African nation. People in Britain will buy 10,000 tonnes of roses today.

Joseph Muchemi, the Kenyan high commissioner to Britain, said: "'Food miles' is a valuable concept but it must be looked at in the whole. It is neither fair nor sustainable to stigmatise certain goods purely on the basis that they have been freighted by air. 'Food miles', or the distance food has travelled, is on its own not a reliable indicator of the environmental impact of food transport."

Hilary Benn, the international development secretary, said that while people wanted to buy ethically and do their bit for climate change, they often did not realise that they could support developing countries and reduce carbon emissions. "Recent research shows that flowers flown from Africa can use less energy overall than those produced in Europe because they're not grown in heated greenhouses. "So, this Valentine's day, you can be a romantic, reduce your environmental impact and help make poverty history. This is about social justice and making it easier, not harder, for African people to make a decent living."