Right. I've been using less powder and have made sure there are no lumps by running the machine for a couple of mins before putting the washing in. (My machine can be stopped to add items at the last minute for a short time after starting the cycle - very useful!), running the "rinse and spin" programme after the washing is complete, and remembering (not always, unfortunately) to wash everything inside out, I have still not managed to stop these blotches on the washing appearing.
I have spent quite a bit replacing the ruined clothes and have now thrown the packet of powder away, still half full. Off to buy the liquid again today.
As for shops which sell things without packaging, where you can refill the bottles, dream on! There is someone planning to open such a shop about 30 km from here, due to open in December, but they will probably be selling nuts and cereals. If they do branch out into soaps and detergents on tap, it'll most likely be the eco-friendly ones. I've tried them and ruined a couple of woollens that way.
I was brought up to be environment-friendly and to avoid waste, and, here in Germany, it is a big deal, which I thoroughly agree with, which is why I tried the powder in the carton in the first place, but I really can't see how throwing away loads of otherwise perfectly good clothes is environment-friendly.