Listed companies: 10% tax exemption, companies holding 20% free float shares are provided 20% tax exemption.

The position is further clouded by the curious share structure of Racal Telecom where most of the free floating shares are US held.

From the March 2008 reshuffle onwards, prospective PSI-20 companies are required to possess a "trading velocity" (the fraction of the company's free float shares which have changed hands over the previous calendar year) of at least 10% so as to safeguard the liquidity of the index.