kvalidir is right
"An estimated one in three adults (36.5%), around 12 million people, had ever taken an illicit drug in their lifetime; three million people (8.9%) had done so in the last year; and 1.7 million people (5.2%) had done so in the last month.
Drug usage is consistently higher for young people than for the whole population. For people aged 16-24, 2.5 million people (37.7%) had ever taken an illicit drug in their lifetime; 1.3 million (19.3%) had done so in the last year; and 700,000 people (11.1%) had done so in the last month.
The survey also estimates that five million adults (15.6%) had ever taken Class A drugs, one million (3%) had in the last year, and half a million (1.5%) had done so in the last month."
That's from
http://www.drugscope.org.uk/resources/faqs/faqpages/how-many-people-use-drugs