Our insistence on distinguishing between moths and butterflies is a bit meaningless. The little white, slim-bodied butterflies that I disturbed in Cupar today, with wingspans just a few millimetres shorter than those of the Orange Tip Butterfly were in fact Silver- Ground Carpet Moths (Xanthorhoe montanata).
They usually fly at dusk, but when disturbed during the day take to the air and fly around for a bit before coming to rest, in the case of the one pictured, on the path under a nettle leaf.
The term Carpet is a bit misleading; in common with over 99 percent of British species of moth they don't eat carpets or clothes. In fact their caterpillars feed on Bedstraw, (Gallium) often referred to as cleavers, something of which most gardeners would approve.
The belong to a very large family of moths with about 23,000 different species called the Geometridae. A characteristic of the caterpillars of this family is that they loop their way along.