I agree you should do more basic training, possibly in your garden where it sounds like you need it.
Just be careful the gundog trainer does not ask you to get physical with your dog as some are very traditional. Some trainers wait for the dog to make a mistake and punish it but If you go down this route it is full of pitfalls and could be detrimental to your relationship.
Punishment can work although there is so much that can go wrong so be real careful.
I would really work on your basics, and control and prevent him having the opportunity to chase birds PERIOD.

I would also work on a rock solid leave.
You are not teaching him much by yanking the lead and shouting NO I'm afraid.
Why not try taking him out on lead and rather than yanking him back, just stand your ground and wait(It may be sometime to start with) for him to finally turn to you of his own accord and the second he does so Mark the moment with lots of praise and a jackpot of real yummy food.
Use something really high value, something he really likes.
By doing this you are teaching him to look at you when the lead goes tight.
Do a web search for Leslie Mc Devvits Look at That Game, that might help