There was nothing wrong at all with the the Kettleworth Peppered Moth work. He put the moths on the tree trunks just to make it easier to photograph, the actual work was extensive and well done. The moths do rest both on the trunks and the leaves and natural selection was in operation. Look here for more:

The Peppered Moth Story, http://www.talkorigins.org/indexcc/CB/CB601.html

in particular:
http://www.talkorigins.org/indexcc/CB/CB601_1.html