We received planning permission for our conservatory but local council asked for exterior bldg materialsamples

They did not tell us when we applied 8 weeks ago that they wld require samples. When i queried permission two wks ago they said they saw no problem with the conservatory. i asked if we cld go ahead with the bldg; they said it would be at our own risk. we have since completed the external structure and now - 8 weeks later - they ask for samples of the materials we are using for the building. everyone i spoke to said this was ridiculous; no websites mention samples ever being asked for. is the council being difficult or is this standard practice. anyone got any knowledge of this; would be greatly appreciated.