In reply to EddInaBox: I'm more concerned with ethics than the law- I think the chance of getting locked up for putting chalk on a route, or even brushing holds is next to zero, but I do genuinely care for our and other creatures' environment.
So let's approach this ethically... Chalk alters the PH balance on cliffs and in soils. If you're one of Steve Findlay's clean-hands chums and don't use chalk then I crumble at your ethically superior feet, but the vast majority of us do use it and this kills almost everything- especially in areas of moorland where all the plants are acidic munchkins.
Brushing, either with hands or brushes does a similar job. If you didn't climb on the rocks then they'd soon grow back under a thick carpet of all sorts of things- especially after weather like we've had this year, so yes you are having an effect on the environment by climbing- even if you're going to 'already clean' areas like Stanage.
People love deluding themselves that they have no impact on flora if they stick to already clean buttresses, but I've seen how fast moss comes back if left alone and how popular crags are indeed dependent on perpetual cleaning, rather than being in some zen end-state of balance.
I know some lichens are very sensitive, perhaps rare and take longer to get established than others. These need protecting, but often it's a choice between climbing or conservation. That's a debate worth having, but don't victimise people because they don't go to honey pots- the issues are exactly the same. There's an argument that occasional very intrusive outings on the rock do less damage than constant little bits of gardening- if a route only gets repeated every 10 years then the flora is never really removed.
We can pretend that we are doing no evil if we don't venture off the beaten track, but that is just patently untrue. Go have a gander at a once popular crag that has now fallen out of favour- you'll be amazed how quickly they return to nature.