John Gregory was a British big band leader in the 60s and 70s. He also performed under the pseudonyms Johnny Gregory and His Orchestra, the John Gregory Orchestra and Chiquito and His Orchestra. A more detailed discussion of his ouvre as a composer and band leader can be found here: http://www.vinylvulture.co.uk/lounge/lounge_2b.php A nice interview can be found here: http://www.vinylvulture.co.uk/interviews/john_gregory.php
Apparently, there is also a pop singer called John Gregory. His official site can be found here: http://www.johngregory.com/main.html. The last piece of posted news on his site is from 2004.