One hundred thousand tourists a year venture from the UK to Kenya for its climate, its Indian Ocean resorts and the wonders of the Masai Mara game park.

But the tourist industry – recently reported to have accounted for 19 per cent of Kenya's gross domestic product – was under threat last night after the latest scare for the east African nation.

Longer term, the cancellation of flights and the consequent heightened anxieties of passengers is another body blow to the airline industry, already reeling from the downturns caused by war and Sars.

But it is the people of Kenya who will suffer most. Tourism is Kenya's second biggest foreign currency earner after tea. The earnings have dipped, however, since the 1998 US embassy bombing and last year's attack on an aircraft carrying Israeli tourists from a resort near Mombasa. The grounding of flights is likely to deter more hardened holidaymakers – likely to includeupmarket tourists attracted by the country's wildlife.

Travellers at Heathrow last night voiced disappointment and alarm over the threat.

A businessman, Anthony Pariola, whose mother was using connecting flights to get to Nairobi, said: "I would rather she didn't go, but she has to because it's a funeral ... I think [the terrorists] have been waiting for George Bush to take a break. I don't even feel safe at Heathrow."

Patricia Siplon, a professor supervising a group of students from Vermont whose trip had been cancelled, said: "It's a tragedy that it's come to this."

Unwelcome ripples from the alert are likely to affect Tanzania and Uganda, though South Africa could benefit from tourists switching destinations. Latin America, which in the 1980s and 1990s was considered largely off-limits to sensible souls, is increasingly seen as a safe haven.

Part of the attraction that Kenya has traditionally held for Britons is the strong links the country has from its "colonial" days, which leads the locals to give overseas visitors a warm welcome.

People who do visit Kenya often choose to combine safari holidays with spending time at some of Mombasa's hotels on the Indian Ocean.