carla: "there's no justice in 60 odd innocent Londoners losing their lives. Or anyone from any other country, for that matter."
"they're not all necessarily innocent"
So, because some people killed 60 innocent Londoners, we jettison justice and fair play, and start holding people for long periods with police in charge.
and since some may be guilty, we are happy to treat the innocents similarly.
Suppose you are a redhead, and in you locality a breakin and murder has taken place. It appears from the evidence that the crime was committed by redheads. Would you be happy with a law giving powers to the police to hold redheads (they suspect) for 90 days. They could suspect you and hold you, during which you will be separated from your children; your job and marriage may get on the rocks etc.
Wwould you hail such a law?
Actually, redheads are easier to spot, but the aim of this law is the Muslims, and there would be many who aren't Muslims but would be punished nevertheless.
Remember the Brazilian being shot dead.
If the police are given such powers, you will eventually find yourself in a police state.