Anonymous wrote:i always thought it was Picadilly Circus aswell, "i went down to the dilly to check out the scene", i know that dilly is picadilly circus, so thats my assumption.
Yes, it sets the scene, but the song doesn't remain there, moving on to Leicester Square and Vine Street. Whatever else it is, I have never felt Piccadilly Circus to be the Main Drag of London. As the name gives a clue, it's circular, so it would be atypical if it were. In this context, the Old Main Drag is just the Central London parade ground in general. Shane keeps it relatively vague because, as Fintan suggests, the universal is evoked from the particular. In other words, the location is, in itself, a comparatively minor character in the song.
The Dilly (as in Piccadilly) is, or was in the 1970s at least, the principal "meat rack" for rent boys in London.