God Bless England
My prayers and those of my family are with Londoners and all of England this morning.
As for a Christian response to terrorism, I believe Paul gives us clear direction about how to handle such evil:
Do you want to have no fear of authority? Do what is good and you will have praise from the same; for it is a minister of God to you for good. But if you do what is evil, be afraid; for it does not bear the sword for nothing; for it is a minister of God, an avenger who brings wrath on the one who practices evil.
London has faced such evil and prevailed in the past. It will do so again.