I have no idea if John Williams is officially influenced by this composer, but one listen to E.J. Moeran made me think of John Williams instantly. Listen particularly to Serenade in G (1948) and it sounds like John Williams from the opening bars. There are other hints of John Williams in many of Moeran's other works too, including Symphony in G Minor (1937). I would just recommend listening to anything by E.J. Moeran. His name has not really lasted through to our modern day, so he is not very well-known anymore, and his music is difficult to find because of that. He lived 1894-1950. Ever since I first heard him, he has been one of my favorite composers, along with John Williams (and specifically because he reminds me a lot of John Williams, though he precedes him). I am sure that any fan of John Williams' music will love E.J. Moeran as well. I actually registered an account on here just so I could tell you all about E.J. Moeran, since I didn't see his name on here. He's just THAT good in my opinion. I don't want his name/music to disappear from knowledge. You can buy CDs of his music here: http://www.arkivmusic.com/ Also, you can download some of his music for free here: http://www.moeran.net/ People have also uploaded some of his music on YouTube:
(the beginning melody of this sounds just like John Williams, though it's from 1937).
