Italy has announced it will start including estimated revenues from prostitution and illegal drug sales in official gross domestic product (GDP) figures.

The country's National Institute of Statistics says starting next year, the GDP result will also include estimates on the value of the black market in cigarettes and alcohol.

The move has been driven by new European Union rules requiring nations to include all activities that produce income in their national accounts, regardless of their legality.

The institute says the procedure will be "very difficult for the obvious reason that these illegal activities are not reported".

The Bank of Italy in 2012 estimated the value of the criminal economy at 10.9 per cent of GDP.

Theoretically, that could mean Italy's GDP result with the new calculation will come in far higher than the government's 1.3 per cent growth estimate.

Eurostat earlier estimated the average GDP increase for EU nations due to the new calculation to be at 2.4 per cent.

The highest rises were estimated for Finland and Sweden at 4 to 5 per cent, followed by Austria, Britain and the Netherlands at 3 to 4 per cent.

The increase for Italy would be around 1 to 2 per cent.

The "grey economy" of businesses that do not pay taxes is already calculated in Italy's GDP and was estimated to be worth between 16.3 per cent and 17.5 per cent of the economy in 2008 - the last year for which the calculation was made.

ABC/AFP