That 'the development be carried out in compliance with the drawings and specifications submitted as part of the planning application'
[i.e. including the reproduction timber sliding sash windows] will doubtless have been a condition of the Grant of Planning Permission.
There is an argument that changing the windows subsequently for a specification that would not have originally got planning approval is itself a breach of planning permission, whether or not the building is located in an ACA.
Would be worth firing off a letter . . . give someone a headache to deal with . . . make a new friend