Big Butterfly Count?

It is usually maintained that UK butterflies are good indicator species of environmental change. There is a scheme to get the general public to do a UK wide survey (supported by Marks and Spencer) based on 15 minutes of counting of butterflies and day-flying moths in locations near them over part of July and August (http://www.butterflyworldproject.com/media/news/articles/countdown-to-the-big-butterfly-count-at-butterfly-world/?id=0000000017). It is, of course, already known that some species (e.g. Small tortoiseshell) are in decline whereas others (e.g. Comma) are expanding their ranges. I am not certain whether the results will actually help to identify the reasons for population changes (these might well vary from species to species) but most butterflies are 'relatively' easy to identify and there are fewer than 60 species to contend with in these islands. The timing of the survey might also be a problem as a number of species will not be visible so late in the season. I suppose the activity might at least stimulate some interest in the natural world.