How Britain lost 'Fortress Singapore'

On the 15th of February 1942, Lt General Arthur Percival signed the largest surrender in British history at Singapore. The city was supposed to be a fortress, but his force of 85,000 men had been defeated by just 35,000 Japanese troops. Little over 2 months earlier Japanese forces had invaded northern Malaya. Thanks to their advanced tactics and training, the Japanese advanced with incredible speed pushing the unprepared British back to Singapore in a so-called 'bicycle blitzkrieg'. When they crossed the Johore straights and captured the Bukit Timah heights above Singapore itself, Percival was forced to surrender. So how did the Japanese defeat a numerically superior force? Why wasn’t Singapore an impregnable fortress? And could the British have held out?