Colour me amazed! I saw a video of some buskers which someone shared a week ago and the tune I know but couldn't remember where it was from, it is a waltz and I thought maybe Swan Lake or Nutcracker but after listening to the soundtracks it clearly was not. At some point I was going to work out the melody on the piano (very basic strap line) and use that to search (there are a few sites which offer this and I have had luck with it in the past). But I just tried humming to Google, I have a sore throat after a minor op, have not long got up, and can't hum or hold a tune to save my life, but low and behold it offered up 3 results and it was the second one.

The Second Waltz, Johann Strauss.

Okay, a very famous piece of music, and a very recognizable melody, but I just thought my warble was so far off that most humans wouldn't be able to tell me what it was!