Lawyers for the three elderly Kenyans - Wambugu Wa Nyingi, Paulo Muoka Nzili and Jane Muthoni Mara - hailed it as an "historic" judgment.
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Groups of dairy farmers have milked supermarket shelves dry across the country in a protest against falling prices.
Seasonal rains have battered the country since late June with more than 150,000 people affected by floods and landslides.
The bus reportedly hit a tree near Russell Square.