Tiny red leaver leaking under sink

[Optiv]

As the title might suggest, I know diddly squat about plumbing.
Under my kitchen sink, where the main water valve is located, there is a grey plastic pipe connected to one of the metal pipes. This pipe has a small plastic nut and leaver (red) on it which started leaking tonight.
I turned on a tap in the bathroom to see what would happen and it stopped the leak - 4 hours later and still no leak from this nut/leaver.


It's got a me a bit worried though as I'm currently broke and without any knowledge of plumbing.
I think the plastic tube is going off into the washing machine, but I might be wrong, and the water is cold.
The only other thing which might be worth mentioning is that I hardly ever use the hot water at this property.


Thank you in advance.

 

[Winston]

Sounds like a washing machine isolation valve. The rubber washer may be on its last legs, Isolate replace washer and tighten back up.

 

[Optiv]

Thanks for the help, Winston.

Question: In the meantime, to stop it leaking, what direction do I turn the small leaver (if that's even going to help it) as it's rather stiff and I don't want to aggravate things further?

 

[Puddle]

If you turn lever across pipe/fitting it will be in off position

just try tightening the plastic nut that is leaking to see if loose
Get a tea towel and twist nut clockwise ,same way as if you were closing a tap,should stop leaking if hand tight,if not as Winston says,new washer

 

[Winston]

If in doubt call a local plumber I often do this stuff foc for oaps or £20 otherwise.