Seems to be effecting both Sky and NOW Broadband customers including myself where I cant access a number of websites.
Here's one Tweet example, where Sky have acknowledged a problem on thier service which would also effect NOW customers.
NOW are always slow in getting the red banner service warning on their Help Centre website pages when it comes to Broadband outages.
I always use Sky Help Twitter to find out about any Broadband issues or outages that they are aware of and acknowledged (where Sky and NOW use the same service infrastructure so normally the problem is mirrored across both Broadband services). .