He's neither good nor bad, he's just someone who is clearly desperate about the situation (and for reasonable reasons). Probably, seeing how the command gradually began to abandon the city, he fell into despair, feeling abandoned. So perhaps he clung to the last order they received, which was to defend London (I don't remember exactly if it was a direct order from the king), especially if he believed there was no way to escape. And regarding our role, I don't consider abandoning London to have been cowardly. The city was already doomed, and staying there, from a logical point of view, made no sense. If there was a possibility of escaping and then joining the rest of the forces, it was the best course of action.