The Germans have a great word for a tune that you cannot shake. "Ohrwurm" or earworm which gets stuck in your head. In this case it's not the last piece of music I heard on the radio before leaving home, it was a radio advert for Shop Small UK, the excellent initiative from American Express which encourages people to only shop in local stores on Saturday 6th December. This is the advert here - the radio version is the same.
Once you've listened to this then listen to this advert from British Airways back in 2011.
I've not had time to research the creative source of either advert but the similarities are quite marked.