Thanks @spikeyxxx , it works in the compositor as you say , I tested it below :

However , I still need it with an alpha background rather than the black so I can use it in Photoshop. But if I remove the black background and save the image , and then drop it into Photoshop , I get this :

Is the blue bloom being calculated and added in the compositor after the render is complete? How do I save this out with an alpha background with the blue bloom showing?
Cheers!