When driving along i have an annoyed spueak/ squealling noise it seems to be coming from back wheels when breaking it will disappear for 10-30 seconds and comes back.

before i had the car it had new brake pads so i took it to the garage and they put some copper slip on which quitened the breaks down because they were very squeaky to start with, it solved that but now i have the squeak driving normally.

Then taking it back a second time they advised me they had adjusted the brakes, but still no joy.

Thanks

It sounds like you could have picked up a stone that has got trapped in a caliper - the squeal when not braking is the symptom of that, though there could be other explanations. Mine seems to suffer from the same thing fairly regularly, so I assume the calipers haven't been designed to avoid it.

If it's a stone, it should go away when it gets worn a bit - with luck, without wearing a groove in the disc. Logic says that it should pop out one time when you go over a bump, but I find logic doesn't apply to annoying things like this.