In the name of Allah, most gracious most merciful, may His peace be upon you and His mercy be upon you. Let me start by mentioning, that by definition no muslim (believer) in his/her right mind would support terrorism.
We muslims, in this time of crisis, have to be protected from rash actions and the MCB should not have made it open that you were sending such a letter. In fact it was wholly unecessary as (like you say in your letter) every single educated Imaam knows his duty to Allah (swt) - to protect the non-believers and believers alike from evil wherever it strikes. Whether it be terrorism, individual or state-sponsored.
The media seized on the letter immediately sensing the furore and instant appeal to those that say mosques are "terrorist breeding grounds". (A statement which is a disgusting untruth - as we all know). They turned it to their advantage almost gleefully in my opinion to sell their papers or get the viewing figures. Islam is being made into a farce by the constant interviews with those who have no learned basis in their faith and have no right or knowledge to lead.
I read your letter, and it of course makes a lot of sense in a closed environment. However it backfired on the community quite a lot. We had badly informed people from every newspaper trying to interview our brothers and sisters who were ill-prepared and caught off guard - unaware of the way their words can be twisted around in print by leading questions.. and they brought out Abu Hamza once again, their "favourite example" and any other person they could find to misrepresent us in a bad light (to get their "reaction")
Please learn from this and know that you should not have drawn attention to this letter because it will be seized by the media and turned into sensational stories without giving your full message. In such times when we are so weakly defended from these hawks whose only thought is to sell stories no matter if they have to lie or misrepresent you to do it, you have to be very careful.
Some media outlets wil print and print with utter glee the fact that the Muslim Council of Great Britain (who will appear to most people to be on the "inside") knows that something has to be done to control these "wayward Imaams" so much, that they had to send letters out to all of them to tell them what to say. In the minds of the ordinary public, it provides the background undertone to satisfy them that the Imaams are uneducated in their own faith, and that we had something to hide in the first place. This does nothing to bring people to Islam. Quite the contrary.
Unwittingly, the type of publicity your letter recieved, regardless of the content (which is all fine) branded every Imaam and every mosque in the UK as incapable of deploring terrorism on their own and it appears to most people from the media that all mosques are partly guilty in spreading terrorism.
I think you are a bit naive in letting this become public. Not only because of the message you sent to the those who dont know Islam through the media, but also the goodness in the message loses some of its punch and authenticity if the disenfranchised youth think it came from a third party "control element".
Plus, those people that call themselves muslim that actually do believe in terrorism.. do you think that your letter would change their mind? They are already lost. May Allah bring them out of their condition (of bowing to evil and disbelief).
I generally support what you are doing, of course it is right to condemn terrorism and we continue to defend ourselves every day in our homes, and in our workplaces doing this very thing by following the fundamentals of our religion. However I ask that the MCB should consider your next move with far more care and planning. Even good intention in this day and age has to be analysed first.
I ask Allah to provide the knowledge and guidance to make the beautiful character and peace that is Islam shine from us all so that we can lead the doubtful peoples onto the true path to righteousness before the last day.
wa Alaikum as Salaam