After trying a few things we came to the conclusion that the Google Play Store was blocking my IP as every other service in my phone worked perfectly and I could access the Play Store OK from other WIFI connections. Emily advised me to turn the router off overnight as that should mean the IP address was reset to a new one, but it did not work as the router had the same IP address. However I have just been away for a few days so I turned the router off while away and having switched it back on last night it has a new IP address and the Play Store apps now update OK. So it seems you will need to turn the router off for a while so that it gets a new IP address, the longer the better until the IP address is renewed. I hope that helps.
Why the Google Play Store blocked the IP address in the first place I have no idea.