Continuity mistake: When Basil is talking to Mr. Hamilton in the dining room there is smoke coming from the kitchen. The next moment he goes into the kitchen and all the smoke is gone. (00:24:00 - 00:25:00)
Continuity mistake: When Basil brings the Hamilton's their bottle of wine, he fills up Mr Hamilton's glass but not Mrs Hamilton's. However, a couple of shots later, we see both Mr and Mrs Hamilton drinking wine from their glasses despite nobody pouring any wine into Mrs Hamilton's glass.
Answer: It's "Leisure Complex" by Dave Gold and Gordon Rees. Can be found on YouTube. The relevant clip is around 25 seconds in.