Lot of rumours this is connected to government mandated orders to remove Huawei kit from their core (O2 are the only major carrier to have Huawei inside their network (not just at the edge level)). Perfectly feasible that some fucking idiot has just done a config wrong and fat-fingered something then rolled it out across the whole estate, but it's not been noticed until now because they only cut the equipment over last night.
Comments
I was having mobile data issues in Sidcup yesterday but that was THREE. Perhaps they use the same infrastructure?