LONDON — British police and security services already have some of the most powerful surveillance laws in the world, with weak judicial oversight and little criticism on privacy issues from a public that generally trusts its government and Civil Service.

Surveillance cameras are everywhere, especially in cities, and there are relatively few restrictions on the mass collection of telephone and internet data by the government.

All of which raises the uncomfortable question of what more can be done to prevent the kind of terrorist attack that killed seven people in central London over the weekend. After three terrorist attacks in 73 days, Britain is engaged in a new debate about balancing civil liberties and security, just days before voting in parliamentary elections on Thursday.

It is a familiar dilemma in the United States, where President Trump’s effort to restrict immigration from predominantly Muslim countries is blocked by courts, as well as for governments across Europe, particularly in France, which has suffered even deadlier terrorist attacks than Britain in recent years.