it looks like fungal spores probably a species of Rust. I'd be tempted to bin them but if you don't want to then you can put them outside in a sheltered space to protect from frost.
certainly there is a risk of the spores spreading the fungus when you water them. water droplets will splash and move the spores about.

Agree. Yes, I would take off the worst affected leaves, leave them outside in a sheltered position and give them a blast of systemic fungicide.

Thank you both for replying. I guess I better dump them, even if I blast them with systemic fungicide is there a risk of it coming back in future

there is always a risk with rusts as the powder are its spores and they may well be in your greenhouse now. they will reinfect sadly. personally I'd bin them. [not your compost bin though - household bin]

A few questions please.
The plants were fine up to a week ago, how did it get in or is it caused by humidity.
I'm new to greenhouse growing, how do I disinfect the greenhouse.
At the moment I have 10 trays of annuals in there, Ide hate to loose them

I would say that it is the humidity in an enclosed space. Having said, some plants will attract rusts and fungus spores no matter where they are. Things like Centaureas and Asters are some. Therefore, I wouldn't want to have these in the greenhouse.

the fungal spores are in the air. on sunny winter days open the door to let some ventilation in. especially true for avoiding mildews [ another fungal group]. I still scrub my greenhouse down with a solution of jeyes fluid.

I have never lifted my evening primroses. They seem to survive.

yes I leave mine in the ground too. though I start seed off in the autumn and overwinter in the greenhouse.