Hello there,
I would start with losing the head collar.
Get a large link check collar to give you some control when you need it, large links so as not to interfere with that beautiful coat. Get out in the garden or stay in the house and concentrate on making putting the lead on fun. Loads of easy training excersises that the dog knows well like sit, down etc and praise like mad. Make these excersises short to begin with, one sit, mad praising, take the lead off. Do it again half an hour later.
I suggest you work up slowly so you are concentrating on walking with a loose leash and the sit command before you even go out on the street if possible. Work in a long "ssssss" at the begining of some of the sit commands and when the dog is listening to that and slows down when it hears the "sssss" change it to a "ssssssteady" in a low, calm voice and slow your pace at the same time.
When you are rock solid on this and the dog is looking forward to having the lead on, go to the front of your house/apartment and get the dog to sit on the pavement for 5 seconds, go straight back to the area you have been training in and reward. Next time stay in the training area, next time go out front and get the dog to sit for 7 seconds, next two times stay in the training area. Next time go out front and get the dog to stay for 9 seconds. Next three times in the training area having fun....you get the idea.
Two things are vital to this working...don't rush it. The dog does not need as much physical excersise as you think as long as it's head is working. If the dog does not get the usual walk for a month, it is worth it.
Second is the reward you are using. If the dog refuses food when it has it's halter on then the food is not the ultimate reward for the dog. If the dog has a favourite toy (ball, rope, frisbee) that it likes to chase, make this the reward the dog only gets when it behaves well on the lead, i.e. if you don't chase cars, you get to chase this and get my attention at the same time. Your dog needs time to learn this so deny access to this toy at all other times.
Give it a try, stay as calm as you can, and take everything very slowly....as soon as we anticipate a problem situation we tend to try and rush the dog through it to get it over with. Getting the dog's attention onto you and slowing everything down with sits and steadys should help a lot.