SIN-KTM Business class A320. Spacious seats nice cabin attentive crew addressing each passenger by name throughout the flight. Flight deteriorated after meal service when the crew allowed the members of several tour groups travelling in economy to come and sit with their friends in Business serving them drinks and snacks subjecting business passengers to a four hour procession of childish mock resentful comments such as "so this is how the other half live". When all the seats were full people then stood in the aisles at one stage there were 15 people in a 12 seat cabin. They were only asked to return to their seats on commencement of descent into KTM. Noisy intrusive and unpleasant. A complaint about the noise to the Chief Purser resulted only in a mute fixed smile. No other airline would allow this. Never again under any circumstances in a premium cabin with SilkAir.