In a medium saucepot, cook bacon over medium heat until crispy. Remove bacon, leaving fat.
Add onion, celery and carrot and sauté until onions are translucent, about 5 minutes. Add courgette, broccoli, cauliflower and red bell pepper and sauté 3 minutes more.
Remove vegetables from pot and set aside.
Melt butter and add flour to pot over medium heat. Stir constantly until a nutty aroma is noticeable, about 5 minutes.
With a whisk, stir in chicken stock a little at a time. Whisk in milk in a slow stream.
Return vegetables to pot, add corn, thyme, oregano, bay leaf and potatoes and bring up to a simmer. Cover and simmer soup until potatoes are tender, about 20 minutes.
Add bacon and season to taste. Remove bay leaf before serving.