YouTube have confirmed that their service is back up and running and service should be back to normal.
YouTube have released the following message: Thanks for your reports about YouTube, YouTube TV and YouTube Music access issues. We’re working on resolving this and will let you know once fixed. We apologize for any inconvenience this may cause and will keep you updated.
Original Update: 2.45pm
We are currently aware of issues accessing YouTube videos. We have established that the issue is not isolated to the Managed Network and will continue to keep an eye on developments and provide any updated information as we receive it.