The Private mode in Safari (iOS 8) lets you browse websites without any trace in the app's history. It's a safe way to browse the web on your iPhone/iPad because it prevents recording your browsing history, storing cookies, website tracking etc.
Enabling Private mode is easy but we just found out recently that sometimes, the “private” link doesn't show up in Safari's tab view. Given that this is the easiest way to enable private mode, it will be impossible to switch between private and normal modes without this link. Incidentally, you might also notice that the “Clear History and Website Data” option (in Settings → Safari) disabled. Fortunately, there is a fix for this. Here's more on that.
Turns out, “Restrictions” plays a role in enabling/disabling the “Private” mode link in Safari's tab-view. If you have website restrictions enabled, there's a possibility that the private mode link will be hidden. Sometimes it looks like a bug too but anyway, here's how to fix the missing Private link in Safari.
Step #1. Open Settings
Step #2. Tap on General
Step #3. Tap on Restrictions
Step #4. Enter the restriction passcode
Step #5. Scroll down and tap on Websites
Step #6. Under Allow Websites, tap on All Websites
Step #7. If that's selected already, tap on Limit Adult Content and then tap on All Websites again
Step #8. Quit Settings and Safari (if it's open.)
Re-open Safari and go to the tab-view (tap on +). Hopefully, you should now see the “Private mode link.
Also, within Settings → Safari, check if Clear History and Website Data is now enabled. Note that you should have visited a few websites (basically, have some history) before the link/button becomes clickable again.
Note that this method only applies when you have already enabled restrictions. If restrictions are disabled, then there is no point in enabling them again and trying this out. However, just to be sure, you can try enabling restrictions and tapping on All Websites option.