Many thanks for the answers so far. I am certainly going to talk to the DH Moth Club. I have several contacts.
I have now got the photograph and the caption. The story becomes even more interesting. The jump actually took place at night!
The caption reads;
"Picture taken on Salisbury Plain 1:30 am. August 14th 1938 after baling out of a Rapide at 20,000 ft at midnight. Delayed pulling rip cord for 15,000 ft or 75 secs by stop watch and flash light."
I have always thought that skydivers, of whom my son is one, are a bit bonkers but this was a pilot for heaven sake! The family who have only just discovered these photos would really like to know more about his life, obviously an adventurous one. Other pictures suggest that, after a career in the RAF between the wars, he may have become an ATA pilot.
If people are interested I will relearn how to post pictures.