Ive seen plenty of photos and Pathe footage of it, I always assumed it was just for the cameras.
put it this way - would you want to up off a rough field right next to a guy with just 10h in a Spit I when it does the lurch? 
"They were expendable" becomes the key phrase. Wartime. Edwards Park talks about those take offs in his book on flying the P39 in the PTO. They hadn't done them stateside but were expected to in the combat zone. His flight lead cut into him just as he left the runway with no speed to move. He had to duck under and then catch him. The next guy caught propwash and augered in.
You basically tucked your wing in behind the lead's wing and kept your eye on him the entire time, raising your gear when you saw his go etc.
When fuel, not getting hit on the runway, and getting a lot of planes together is the issue, the risk is secondary.
Think about those Spits all going at once on those grass fields in England. When their entire flight to France and back is going to amount to about an hour and a half, taking the time to go one at a time and form up would really reduce the distance they could go.
