Snowman wrote:

There's no nut. The tap is one where a quarter turn turns it off. ie when
the oval bit you turn is in line with the pipe, it's open, if you turn it
quarter of a turn so that it's crosses the pipe it's closed.

It sounds suspiciously like a gas tap to me. Anyway, there may well
be a nut on the back of the tap you could loosen (just a bit mind).

Nick