Both activities are worth 0.7 per cent of GDP, equal to agriculture, accommodation services, such as hotels, or publishing industries, including newspapers and magazines.
European Union (EU) rules mean the Office for National Statistics (ONS) will for the first time have to include illegal activities in its official estimate of the total value of UK goods and services, also known as gross domestic product (GDP).
Based on 2009 prices, the ONS has estimated that prostitution will add £5.3bn to GDP, while drugs will boost the economy by £4.4bn.
In the years between 1997 and 2009 the impact ranges from £7bn to £11bn, statisticians said.
Campaigners against violence against women said it was “frightening to see such human tragedy financially valued”.
A spokeswoman for women’s charity Eaves said: “Given that the entry routes to prostitution and the barriers to exiting prostitution are known to commonly include childhood sexual violence, domestic violence, neglect, abuse, poverty, destitution, coercion and addiction – it is humiliating and frankly frightening to see such human tragedy financially valued and counted as ‘productive’.”
For measuring the contribution of “prostitution services”, statisticians will assess the value of rental of brothels, sales of condoms and sales of clothes worn by sex workers.
When assessing the impact of illegal drugs, the ONS will consider production and sales of crack cocaine, powder cocaine, heroin, cannabis, ecstasy and amphetamines.
The data will class growing drugs or importing them as “production” and selling them as “income”.