As you have said, the problem arises because he has not been used to the lead and he loves running free (as do all springers). You have to get it into his head that walking on the lead is something he has no choice about and show him that it can be pleasureable. I would not use an extending lead or a harness, as I feel that they just teach a dog to pull. Do you know how to use a chain collar? If you know how to use one I would do so but don't use it unless you know how!
I would only exercise him on the lead until he accepts that he has to do as you say. Use treats and a lot of praise but don't let him stop, even if that means you have to drag him (not on the chain collar though). If he totally refuses to follow turn round and go back home. He wants to go for his walks and will gradually learn that in order to do that he has to go on the lead. Walk straight from home, don't take him to the park in the car. You will need to take him out very frequently as he needs a lot of exercise but if you stick to lead only exercise he will soon learn.
Good luck