The UK system of company taxation. This tax is levied on the trading profits of all companies, with slightly lower rates for smaller companies. The corporation tax was introduced in 1965 with the structure of a classical tax system in which companies were subject to tax on their profits and shareholders were also liable to income tax on the dividends received. The corporation tax was changed to an imputation system in 1973, so that a shareholder receiving a dividend was entitled to an income tax credit representing the corporation tax already paid. The classical system was reintroduced in 1999, with the abolition of advance corporation tax.