even if the external aerial is broken, flapping about or non-existent they could say you are using an indoor aerial.

if you use a monitor with no TV tuner they wouldnt be able to make you buy a TV license. some LCD TV's on the market have no tuner in them so you could get something like that.

even if you satisfy them they will probably keep on trying to catch you out in future though in case you've gone and got a portable or whatever