Excerpt:
For more than a century, a point on the top of a hill in south-east London has been recognised as the centre of world time and the official starting point of each new day.
But now the supremacy of Greenwich Mean Time is being challenged by a gargantuan new clock being built in Mecca, by which the world's 1.5 billion Muslims could soon be setting their watches.
Due to start ticking on Thursday as the faithful begin fasting during the month of Ramadan, the timepiece sits atop the Royal Mecca Clock Tower which dominates Islam's holiest city.