Commuters on one of London’s busiest commuter train services were given a rare reason to smile after their conductor put on an impromptu music quiz.

Passengers who take to Twitter to write about South West Trains are more likely to complain than with any other UK line – but among the grumbles this morning, people on one service said the tannoy-based test had genuinely brightened up their day.

One passenger on the 7.59 from Ascot to Waterloo told the Independent the packed carriage was pervaded by the “standard grumpiness” until the train guard revealed they would all be “doing a quiz today”, with the question repeated at each stop for the benefit of newly-boarded customers.

Ollie Parke, a 27-year-old consultant who works in central London, said: “I thought it was funny, and it certainly cheered people up. A few strangers were discussing their answers, and everyone left at Waterloo with a smile on their face.”

While Mr Parke had never experienced anything like it before, the morning music quiz appears to be a relatively regular occurrence. Lisa Blythman-Wood wrote: “Got my favourite guard on the 8:18 from Staines – pop trivia quiz time.”

The question posed by the guard was: “What is the name of the song which features the lyric: ‘Who put a real live toad in the hole?’”

If people thought the answer might be a recent hit they would have been disappointed – it's actually from a 1960s novelty comedy song entitled “My Brother”, by the late Carry On actor Terry Scott.