I’ve now got a stick neck from trying to view that photograph in its 90º rotated portrait format!

Is it the Portland Road on the Co-Op van that makes you think that it’s Portslade? Assuming that the building behind the Dragon is a hangar, I can’t think of anywhere in Portslade that such a building is or has been. But I don’t claim to be an authority on Portslade. Maybe try posting the image on the Sussex History website?