Hi
I think you have a case of possessive springer syndrome! They think its much more fun to extend the game and hang on to it. One way is to sit the dog down, walk off 5 yds then whilst still walking command heel. Practice this until he will catch you up and walk at heel without running past or anything. Make sure he is 100% good at it. Next stage is to give him a dummy whilst he is sat, walk off in the same way and command heel. Hopefully the routine of previous practice will work and he will catch you up and walk with you. Keep walking, changing directions sometimes as he gets better but dont be in a hurry to take it off him as this is often what started the problem in the first place. Ideally carry on walking and reach down to remove dummy gently. Progress to coming to a standstill, waiting quite a while then sometimes removing dummy, sometimes walking off again then removing it somewhere else. Point is to get him following you round and dont take it from him too readily. Lots of praise when he improves. Let me know how you get on and good luck
ps I know how you feel cos I had just the same thing with mine. Expect slow progress and be patient.
John