The consensus is that it was only a matter of time before the UK was hit by the sort of terrorism that has hit other countries. There is also a pretty widespread acceptance that, dreadful as yesterday's events were, particularly for those people caught up in it or affected by it, then if that is all the UK faces, we will have got away lightly.
One of the odd things that I noticed in people talking about the events of yesterday, and the people who might have been directly affected, was how many people had "lucky escapes" - a woman who chose to go into a different carriage because the one she first went to was too full - somebody who chose to work from home that morning, and so was away from the affected area - and so on.
There are two possible conclusions - the relative weight you give to one over the other will depend a lot on your worldview. The first is to attribute these "lucky" escapes to providence - effectively saying that God overruled to keep me clear of these incidents. A corollary of this is that you are then compelled to conclude that God also overruled to determine those people who were caught up in it - who probably made a series of just as arbitrary decisions, which led to them being in "the wrong place at the wrong time". Whilst those people who had narrow escapes can be thankful, is it right for those people who happened to be affected to be resentful?
Theologically, this perspective is correct if you believe in a sovereign God. However, in coming to this conclusion as to how God acts, it is important to bear in mind what Jesus said about both natural disasters and human tragedies - it isn't possible to know what God's purposes are in allowing these things to happen, but we all need to be aware of the fact that death walks close to us all the time - and furthermore, that death isn't the worst thing that can happen to you.
The alternative is to say that everybody's lives are really a whole series of co-incidences anyway. What decides which carriage of a train I will go in? What determines which train I catch, when there is one every five minutes? What determines whether I will only go into work this afternoon? Well, it's all arbitrary and certainly hardly predictable. Some people had a lucky escape; other people were unlucky to be affected. It's just one of those things.
In some ways, since in most circumstances we can't have any idea what God's ultimate purposes are in what happens, even for Christians this may be a safer perspective. After Hitler survived an assassination attempt, he concluded that it was his destiny to survive - and he pursued his programmes of genocide all the more vigorously. It's probably safer for all of us to accept we can't know what God's purposes are than to try and work out exactly what God may have had in mind when he allowed something to happen.