The city council uses the following coat of arms:
I've found this flag-like image on internet, but it seems to be just a logo:
I decided to make a design with the key symbolism of the coat of arms, but with vexillological appeal:
The three diagonal stripes represent the three rivers that cross the city: Irwell, Irk and Medlock. The blue glode represents the role of world-level trade center. The worker bees is commonly used as a Mancunian symbol as the birthplace of Industrial Revolution.
A simplified attempt, with just one worker bee:
One thing that I like in the designs (my favorite is still the first) in the circle incidentally tangential to the thicker diagonal stripe formed by the three thin diagonal stripes and their interspaces.
Comments and suggestions are welcome.
Sorry for the delay in publishing this post.