Thanks everyone. I think what I'll do is 'phone them and tell them it has to be there as part of the building regualtions. I'll tell them if they want it removed, they'll have to ask the agency's permission, but that I doubt that this will be given.
Then I'll cautiously approach H (who I think should have blinkin' well asked me in the first place) and ask him to put it back. If he refuses I'll pay for the agency to reinstate it.
Does that all sound okay to you?