Theresa May raised the prospect of a review of Britain's counter-terrorism strategy after the London Bridge attack.
Here is a summary of the main powers and tools currently deployed by authorities:
:: Arrest and prosecution
Counter-terrorism arrests have been running at or close to record levels in recent years. Of the 260 arrests for terrorism-related offences last year, 96 had resulted in a charge by the middle of January. Of those, 79 were terrorism-related and 17 non-terrorism-related. Others were released without charge, or bailed.
:: Electronic surveillance
Security services can deploy a range of tactics under the Investigatory Powers Act. The techniques, which officials say are critical to national security investigations in the digital age, include: hoovering up data relating to phone calls, emails and text messages; intercepting suspects' communications; and hacking into their devices such as smartphones and PCs.
Under the Terrorism Act, officers can stop individuals at ports, airports and international rail stations to determine whether they appear to be involved in terrorism. Last year, nearly 20,000 people were examined under this power.
:: Terrorism prevention and investigation measures
TPIMs are used in cases where someone who is judged to pose a threat to security cannot be prosecuted, or in the case of foreign nationals, deported. Subjects can be placed under restrictions including relocation to another part of the country, wearing an electronic monitoring tag and limited use of computers and phones. At the end of November last year, there were seven TPIM notices in force.
:: Measures to disrupt the return of fighters
Authorities can call on a number of powers to block or manage the return of UK citizens or foreign nationals suspected of engaging in terrorist activity abroad.
:: Powers to seize passports or deprive citizenship
Police can temporarily confiscate the travel documents of people suspected of intending to travel to engage in terrorism-related activity abroad.
:: Air strikes overseas
The Government says it is vital for the UK to retain the right to deploy lethal force in self-defence and as a last resort against terror targets abroad. In September 2015, it emerged that an RAF drone had killed two British jihadists in Syria the month before.
:: Anti-radicalisation schemes
The Prevent programme aims to intervene early and provide support for those deemed to be at risk of being drawn into violent extremism. There were around 7,500 referrals to the initiative in 2015/16. It has been credited with playing a role in disrupting more than 150 attempted journeys to Iraq and Syria. Home Secretary Amber Rudd said there would be an "uplift" in the programme.