Outside tap isolator not working

[Vicario]

The isolator on the long pipe (screwdriver) is the hot feed from the tank upstairs. You can see that the lower one is taken from the cold main where the bigger stopcock is.

 

[Burnerman]

The mystery deepens, I think.....I would have expected the feed from your loft tank to (presumably) the bottom of the copper cylinder to be piped in 22mm - it looks like 15?
Anyway.....you say the bottom stopcock is controlling the incoming main, it then tees left and right, the left heading to the dishwasher / washing machine supply but before that, teeing upwards to the second stopcock.
You say after that it heads outside...have I got that right?
No way the second stopcock can be fixed with a screwdriver......unless it wasn’t closed off in the first place, of course!
John

 

[Vicario]

Yes. There is a hole behind the dishwasher (on the left of the picture) where it goes through a piece of plastic pipe to the outside tap. You can just see where the other branch of the mains pipe goes off to become the rising main (under the blue isolation tap for the dishwasher).

 

[Burnerman]

Aha, is that a chrome isolator valve I see, directly behind the dishwasher take off?
John