At what point exactly in George and Lynne's lives does this occur? Didn't something similar happen just yesterday? Or even if there is a long gap between events, does George not remember the last time a local art class was mentioned? He was shocked then and now he is angry. He must be on some heavy medication.
If we are to take George's memory loss for granted, we must ask the question of what sort of food are they serving at this art class as Lynne is piling on the pounds. Perhaps the module is about Renaissance painters and Lynne has taken this very seriously. If that's the case she must have known she was going to be a nude model. Of course she knew, she told George yesterday. Either that or they are making counterfeit copies of Beryl Cook paintings.
Where is Lynne hanging that dress? She hasn't gone upstairs yet she is insisting on taking her dress off immediately. Is she trying to cover up a scent? Were the art class building up an appetite by smoking some illicit substance. Lynne must be hanging her dress in the broom cupboard. The musty smell will cover up the hint of 'jazz' cigarettes on her clothes.