When officials of French nationality of international organisations have income other than the official remuneration they receive in this capacity, this remuneration, where it is exempt from income tax, is nevertheless taken into account insofar as it would have been taxable, with a view to determining whether the taxpayers concerned are liable to income tax on the basis of this other income, subject, where applicable, to the application of international conventions relating to double taxation. If so, the tax is calculated by adding the remuneration to the taxable income and making a deduction from the figure obtained in proportion to the amount of that remuneration.