Apps won't install or update on wifi

Hi everyone,

I'm having an issue at the moment where apps just will not update or install when connected to a WiFi network but are fine on mobile data.

I open the App Store and go to update one of the apps based on the notifications but all I get is the spinner. Same with installing new apps. I get the circle with the stop button but no progress whatsoever.

However if I switch to mobile data then the downloads start immediately. It's as if the WiFi connection can't connect to Apple servers. Along the same vein, I cannot check for iOS updates. I simply get the error message

Unable to check for update. An error occurred while checking for a software update.

This has happened across multiple WiFi networks, in different locations, and I've asked a number of people who all have the same issue.

I've tried resetting network settings, modifying DNS and using static IPs but to no avail.

I'm on a UK iPhone 6s, iOS 9.2.1.

Device bought directly through Apple.

Any help would be appreciated.