Sage advice via The Guardian...
"Wild flowers According to Dominic Price of wild plant protection charity Plantlife, "it is not normally an offence to pick the 'Four Fs' - fruit, foliage, fungi or flowers - if the plants are growing wild and it is for your personal use and not for sale." Dozens of rare or endangered plants - from the lady's slipper orchid and adder's tongue, to threadmoss and sandwort - are, however, protected under the 1981 Wildlife and Countryside Act, so pick those and you could face arrest (though you're unlikely to stumble across too many of them). Whatever you do, don't drag up the whole plant to resettle it in your own garden - the law firmly forbids the uprooting of any wild plant."
http://www.guardian.co.uk/law/2011/mar/16/rules-picking-wild-flowers