Prostitution and the import, manufacture and consumption of illegal drugs like crack cocaine and heroin will be included in the official estimates of Britain’s economy, the national statistics agency said on Friday. Some of these activities, like prostitution, are legal in certain European Union countries, leading the agency to say comparable figures were needed. Such information is used to assess a member state’s contribution to the European Union budget. The agency said the new estimates also seek to get a more realistic picture of the economy — warts and all. “As economies develop and evolve, so do the statistics we use to measure them,” said Joe Grice, the chief economic adviser to the Office for National Statistics. Illegal drugs and prostitution are already measured in Austria, Estonia, Slovenia, Finland, Sweden and Norway, the statistics office said in a report. In Britain, they would add approximately 10 billion pounds ($16.7 billion) to gross domestic product in 2009. That remains a very small portion of the overall G.D.P., which now stands at £1.5 trillion.