This problem plagued me last summer, and has started again.
Fortnightly collections. We are avid recyclers and composters, so what goes in the bin is nappies (double bagged), plastic packaging, and meat leftovers. All in black bin bags, not thrown straight into the bin.
I clean the bin out straight after it has been emptied with bleach and water, and throw in some Jeyes yellow granules that are supposed to keep it fresh and lovely.
And yet still the maggots come by about day 10.
The council tell me that it is impossible for maggots to get inside the bin if the lid is shut, which is nonsense on my experience.