Intelligence agencies in the United Kingdom are doing the best they can to prevent terrorist attacks, but have relatively limited legal tools to do so, Law and Home Affairs Minister K. Shanmugam said yesterday.

Asked if the agencies were slow to act on intelligence and were playing catch-up, he told reporters that they receive thousands of reports, and have to prioritise to identify who to go after.

"Frankly, they don't have the legal tools that, for example, Singapore has," he said, noting that Britain has, under the framework of freedom of speech, allowed extremist preachers who have "poisoned many Muslims".

With many sections of society exposed to such viewpoints and ideas, Britain's legal tools for agencies to intervene are relatively limited, he added.

He said agencies in every country face difficulties, particularly in other countries, given their size.

"So are they playing catch-up? They are being left with the very difficult task, so don't blame them," Mr Shanmugam added.

To nip in the bud the conditions that could lead to radicalisation, Singapore adopts "activist state intervention" to foster integration, he said.

"We prevent extremist teaching. We have laws that allow us to intervene much earlier than agencies in other societies can," he added.

Even so, people should not assume that nothing will happen, Mr Shanmugam warned.

Asked if the latest attack in London impacts a terrorism threat assessment report that the Home Affairs Ministry released last Thursday, he said the assessment remains unchanged - the threat to Singapore is at a fairly credible level, and the country must remain vigilant.

As for whether law enforcement agencies will ramp up security after the spate of attacks elsewhere, he said the measures in place are at an appropriate level for the current threat assessment.

The threat to Singapore is assessed on a very regular basis, he added. "I cannot go into the details, whether every day or every week, but you can be sure that we are watching it closely."