The post above by 'qwertzguy' about checking my email for the "App Store Connect: Your app ..." really helped. That email had gone into my unimportant email so I had missed it, and it explained that:
"ITMS-90809: Deprecated API Usage - New apps that use UIWebView are no longer accepted. Instead, use WKWebView for improved security and reliability. "
My app contained UIWebView to support iOS7 on the iPhone 4 (and with the WKWebView for iOS8+). I removed the UIWebView and the app was then accepted in the app store.