To be honest I don't see any NTL stamp... only CE which is basically a claim by the manufacturer that this thing conforms to some standards without precisely stating which.
Apparently this is a one-of-a-kind item produced by an artist with a fairly twisted sense of humor rather than an actual product.
British humour, old bean. We're usually the only ones who laugh!
Neddy Seagoon: "What are you doing down there, Eccles?" Eccles: "Everybody's got to be somewhere!" - The Highly Esteemed Goon Show, 1950's BBC Radio.
or-
"Now, children, how would you like two daddies? On the chair, behind the door. Hey diddle-diddle! Here comes poppa, So up with your chopper, And split him dahn the middle!
- 'Uncle Rubbish', spoof 'BBC Radio Childrens' Hour' presenter, [aka Peter Sellers]. [1958]