Looks like a BT66 (block terminal 66), usually fitted externally and used as the transition point between an underground cable and 'internal' type wiring..it is common though that a cable coming out of the BT 66 would terminate at the NTE5 master socket
I think the 'bit of string' is a retaining strap for the lid, so it doesn't get lost
That makes some sense as I have my phone from an underground cable. Although I think that box preceeded that cable when the phone came via pole to the roof.
Out of curiosity anyone know what this is. I have a grey BT branded box immediately before my master sockets (2) its oblong but also slightly triangular with a piece of string/cord coming from the front to the bottom.
do you have 2 master sockets? do you mean one actual master and and other NTE5 used as an extension socket?
2 phone lines 2 master sockets. The first master has 3 extension sockets which is where my noise problem seems to come from.
Just a BT66, normally you find them outside but I've come across them inside, usually in businesses such as warehouses but from time to time inside homes, usually as a result of a person building a conservatory or porch on the front of the house.
Underground cable seems the best explanation as I don't have a porch/extension and I'm fairly sure I'm not a warehouse 🙂