I appreciate your comments on the tug back method Cazza and Jayne as I've been struggling with it a bit myself. It isn't a hard tug at all or a yank, I would never do that - it's more of a slight pull of the lead, but I still don't like doing it and have been worried about it breaking the bond between us (as well as it not actually being that effective!) In terms of it putting pressure of the neck, that's a concern too, but when she's pulling like mad and choking herself then that can't be good either. I've tried using a harness instead of collar/slip lead, but it makes the pulling much worse.
The thing is, she can walk nicely with just a simple 'heel' command and nothing else, but then she sees a bird and it's all out of the window and that's when the pulling/spinning/lunging starts. There's been quite a few times that I've found myself 'stuck' on a walk where I need to walk her home on lead, but her head is just gone and she can't focus on anything other than 'must. chase. bird' I have picked her up on occasion and carried her home as I didn't want to reinforce the pulling, but I must look like a madwoman!
I think we really need to tackle this bird obsession first, and then go back to heelwork as she can do it. I've been thinking about only taking her for a walk in the evening (when her feathered 'friends' have gone to bed) until we figure out a way to make ourselves more exciting than a seagull...