I guess you're really making a reference to Anton's "issue" last week rather than sounding surprised at Anton wearing a blazer, but his outfit this week was directly based on Bing Crosby's in the film High Society, which is where the song True Love comes from. Fiona's costume had a nod to Grace Kelly's in the film too. It is a yachting costume from the 1950s (?) as they sing the song while reminiscing about their trip on a yacht called the True Love.
(Terry, definitely not a 1920s Great Gatsby style costume, sorry)