It may be prudent to invest in some pepper spray, there are brands especially designed to repel dogs; if you don't have any and the situation is desperate then jam your thumb in its eye as hard as you can until the eyeball bursts, this should cause the dog to release its grip.
it is illegal to carry around pepper spray in the UK
 
	 
  
 
		 
 
		
 
 
		 
 
		 ). Usually puts a dog out of action with a decent kick.  Horrible thing to have to do though kick a dog
). Usually puts a dog out of action with a decent kick.  Horrible thing to have to do though kick a dog  but desperate situations ask for desperate actions.
 but desperate situations ask for desperate actions.  
 
		 
 
		 
 
		 
 
		 
 
		 
 
		