How to stop my dog barking and growelling at other dogs

So ive tried using the clicker and giving her a treat  she still is quiet reactive  i deffo couldnt walk past a bigger dog without her giving it the big i am can my dog get in trouble  like someone could pass her of aggressive  she has only recently in the past year become  like this  to bigger dogs i can walk past little dogs and she is fine  just need some and as many different ideas as possible   the only thing i can think as to why she barks and  growls is because the feild i take her on she sees it has her back garden  (live in a flat )  even though its a public field

I think Liz is the person best placed to answer this.

I'm sure she'll be along soon with some very good suggestions.

I have this exact issue with Bailey my Staffy and have adopted a few tactics to deal with it:
1. When walking in new areas or in town where there is a good chance of meeting all sorts of dogs I put a muzzle on him, to keep him and other dogs safe.  
2. If possible keep a distance from other bigger dogs, one that your dog is comfortable with.
3. Try to avoid narrow pathways which might pose a problems if a big dog comes along in the opposite direction.
4. However if this should happen I usually do a quick turn around if the coast is clear behind me.
5. If you have dogs approaching from front and rear I will sometimes pull the tube scarf he wears around his neck over his eyes to keep him calm and then ask him to sit whilst talking to him in a friendly voice.  I also call to the other dog owners to put their dogs on a lead or to call them off if they are off lead and approaching my dog.
6.  If he does have an angry lunging episode one day I usually keep him away from other dogs entirely for a few days to give him time to regain his composure.
7.  Keep up with training such as asking him to look at you to keep his attention away from other dogs that are approaching.  
8.  Every time he has a calm experience passing another dog I give lots of praise and a treat.
Using a combination of the above tactics he is tons better than when I first adopted him from the RSPCA.  However after three years I have now accepted that he will always have an issue with bigger dogs and accept him for who he is now.  A very lovable boy.

Very good answer - thank you!

I would heartily agree with the muzzle until you can sort something out. Muzzling isn't an indication of aggression (although some people do see it that way), but it does help to a) keep other dogs safe and b) make people aware of a potential problem. Nowadays, with the law as it stands, someone only has to say that feel genuinely threatened by your dog's reaction, and the police could become involved.

Muzzle training, done properly, is easy & non stressful for your dog. It also helps you to relax, and that relaxation will be passed on to your dog. ALWAYS use a baskerville-type muzzle - that way your dog can pant, drink & eat treats.

I also agree with treats, although I wouldn't personally cover my dog's eyes as that could make them wary of whatever is around them. Obviously if it's good for your dog, that's great, but many dogs would react more to some 'threat' that they can't see!

I feel the best way is to put your dog in a sit, offer a treat, but don't let it go and tell him to 'watch me'. keep waving the treat in front of his nose & then to your face. Once the other dog has gone, give the treat, and plenty of praise. It might take a few tries, but it usually does help after a while.

Some dogs do always retain a certain aversion to other dogs, especially dogs of a certain size or 'type'. There's not much you can do about that, but if you can get him to watch you instead of the dog, 9 times out of 10 you can avoid a 'situation'.