A little update:

He still likes the birds, sees them an gets excited, tries to chase, but not quite so blindly frenetic.

I've gone with the long line option, and he is coming back better when I call, but not everytime yet.
However, with the whistle, he's there and waiting for his extra special treat (my brother suggested a tiny bit of chopped up sausage), we went with whistle always means sausage and it only happens rarely (Its not a healthy treat). But I'm sticking with the long line for a while yet.

He's calmed the barking in the back garden down, a couple of occasional yaps and stopped (so far) barking out of the window at the birds - I went for a quick squirt from a water pistol for that one. It may return and I work with a loaded water pistol at my side.

Walking wise, we still do have the little sessions of excited yipping, but is not for the whole walk and the howling has subsided....for now....

I've 3 weeks more of my current puppy training class (which he was doing very well in except for the bird recall issues), once this one has finished I'll take a look at the gun dog trainers to see what extra bits of advice they may have.

Thanks for all the advice, its been very helpful!

Today chasing snow flakes is far more fun than chasing birds....