The European Monitoring Centre for Drugs and Drug Addiction press release on trends in magic mushroom consumption by young people across Europe has this to say:
Prevalence estimates on the use of magic mushrooms in the EU are considerably lower than those for cannabis, but are similar to those recorded for ecstasy. Surveys among school students (15–16 years) across Europe report lifetime use ranging from 0% to 8% for both substances, although more typically prevalence lies between 1% and 3%. One positive finding is that most use of magic mushrooms is experimental, with regular use relatively rare.
Among school students, lifetime prevalence of magic mushroom use equals that of ecstasy use in the Czech Republic, Denmark, Italy, the Netherlands, Austria and Poland and exceeds it in Belgium, Germany and France. The highest lifetime prevalence of magic mushroom use is recorded in the Czech Republic, the Netherlands, France and Belgium (between 5% and 8%) and is lowest in Cyprus, Finland and Romania (below 0.5%). [more]
The full report can be found here. They note moves by the UK government to tighten the law around magic mushrooms, and say that reports:
suggest it has had an impact on the availability of magic mushrooms and overall volume of Internet sales.
The following graph gives some indication of prevelance data for different European countries.