Today, 2,000 known terrorists are operating in Britain, and authorities suspect that there are 2,000 more they don't know about. Those sobering statistics, as well as the nation's history of being a target of the IRA and radical Muslim groups, have led the government to hit back hard with strong security measures.
"Because the UK has experienced more terror, they've adopted more Draconian laws," said Richard Clarke, a terrorism expert and consultant for ABC News. "They've made some tough decisions."
The most visible of those decisions is a network of more than 4 million closed circuit television cameras blanketing the country -- a virtual eye covering train stations, airports, streets, and other landmarks.
Control rooms are located in every British city and major town, pulling in the video feeds to gather intelligence and track terror suspects.
In London, a person walking the streets is filmed or photographed an estimated 300 times a day, and new technology promises to analyze all those images to give the government an even more powerful tool.
The new technology is designed to monitor suspicious activity, such as someone leaving a suitcase unattended in public. It would identify the abandoned suitcase, and then follow the suspects as they walk away.
All of these security measures have often come at the cost of personal freedoms.
The 2005 London subway bombings led authorities to crack down on speech that promotes or seems to promote terrorism. The government has deported the radical preacher Abu Hamza, among others, for such speech.
Police can hold terror suspects without charge for up to 28 days, the longest amount of time in the western world.
And while the government denies it, terror experts say that British authorities use racial profiling to track citizens who have no previous terror record.
For example, people coming into Britain from Pakistan are far more likely to be stopped, questioned and, with additional warning signs, placed on watch lists.
U.S. citizen Faisal Shahzad, who was arrested in connection with the Times Square bomb plot, had recently visited Pakistan before last Saturday's attempted attack.
"It's finding the enemy within, people with no record," said Margaret Gilmour, co-author of 'The Terrorist Hunters.' "[The people are] mostly from Pakistan, Yemen, Somalia, traveling home -- supposedly to see relatives but actually to train for terror."
Police also have wide powers to stop and search people on the street, and Muslims are searched far more often than non-Muslims.
As intrusive as the security measures are, polls show that large majorities in Britain support them, seeing these steps as an acceptable price for safety.