When I referred to organisation I was referring to the members and the trustees.
After all, the organisation itself is made up of individuals.
In my opinion, if someone is going about their evangelical work and gets mugged or attacked, that is not a reasonably foreseeable consequence of doing the work and would not be as a result of any negligence on the part of the trustees or any organising members.
It may be that the trustees are liable in negligence if they fail to provide training or a safe system of work but for someone to get mugged for example, whilst going about their duty, I cannot see how that would be the fault of the trustees. For example, if a postman got attacked and robbed, it would not be the fault of the post office.
For the trustees to be liable, there has to be a duty of care and the duty of care has to have been breached. Whilst there is a duty of care here, I cannot see that if someone gets attacked, that duty has been breached.
If the individual was not warned of the risk of being attacked when going about this work, I cannot see that the trustees would be liable for that either. There is a possibility that someone might try to bring a claim but I think it unlikely in the extreme that it would succeed.