Hi, I'm just about to fit my rear lowering springs but the original mounting isn't holding them in place as the bottom coil isn't as tightly wound as the original springs, any suggestions please

If I follow do you mean the plastic retainer isn't locking against the bottom coil and you can lift it over the top?

Yes exactly that.

Ok I wouldn't worry about it too much, with the spring in position on its rubbers and the retainer in place the spring can't go anywhere, even with the weight off the wheels.