Thanks for the info. I do remember the names of those dredgers you mention. I did recognise Bill Cunningham, Same Jupe and Willy Ross because they visited our house many times. We had many happy adventures in the caravan with dad, including accidentally driving onto the runway at Heathrow Airport! This was back in the day, when security wasn't so tight.
Hopefully, I'll find out who the other two in the photo are. It would be nice to know.