Dear Sir Ian,
I've always believed that yours is the most difficult job and this has never been more true.
I am not much of a politician, but I do recognise that people have ulterior motives when they demand your resignation, or they simply don't understand the pressures under which you must work. Some have no concept of how difficult your job is and that we don't live in a perfect world in which everyone is 100% safe and no-one is inconvenienced in any way at any time.
This much I know for sure. Whatever mistakes were made on the day that Jean Charles de Menezes was killed, none of your officers set out with the intention of killing an innocent man. Their overriding intention was to prevent another terrorist atrocity and, in that context, any other outcome was preferable. They showed enormous courage in the face of grave potential danger, when self-preservation would dictate running in the opposite direction.
Had they indeed prevented a suicide bombing that day, no-one would be complaining about how they dealt with it.
In the UK we do not have significant experience of dealing with suicide bombers, and therefore this is a learning process for everyone. We are in a strange, treacherous new world, with limited resources and no margin for error.
If anyone is to be blamed for the death of Jean Charles, it is the July 7 bombers, who have made all of us in our relatively easy-going society afraid, tense and suspicious.
Whether this was deliberate on their part, I do not know (I hesitate to attribute this success to them, because they were not very bright), but it is a consequence which we must all come to terms with.
Therefore, I urge you to not even contemplate resigning, but to push on with the most difficult (and sadly, thankless) job of keeping us all safe.