I don't think I'd ever actually do it though. I sorta like the open access sites a bit wild and wooly. Two of the one's I've been most frequently tempted to trim are those at Greenlee Lough and Simonburn Common , but they both seem quite content with the covering, so I aint going strimming or clipping. As they say in some quarters, "The Bushes Scream while my Daddy Pruuuuuunes..... For this reason, the deadly gorse at Weetwood 5 should stay in it's spikey splendour.
Mind you, there are places where I reckon the foliage should be removed, such as at Buttony, where the pine trees are a bit too intense. Also, anywere where there is bracken. All bracken is vile and should be strongly discouraged. I'd be quite happy with a job as a bracken clearer.