Magic mushrooms are legal in the UK as long as they are not prepared in anyway (eg drying, freezing, made into soup, a dash of red pepper with a sprig of parsley on top and a light vinegerette dressing...etc...etc), so theyre not really that dangerous to you physically, but I've heard stories of people having 'bad trips' that can affect you mentally/emotionally. I'm not talking serious damage here but just the same as having any other bad experience would do (getting lost in the supermarket as a child for example), so there isnt too much to worry about. A bad trip usually puts people off them anyways, and because they arent addictive (as far as im aware) you can get put off them as many people who took food tech in my year were put off McDonalds after watching a vid on how theyre made!!! Hope I've been a help.