Shares in Britain's largest package tour operator Airtours Plc fell by as much as eight percent on Monday after Carnival Corp said it would sell its 25 percent stake in the company. The stake was worth around 358 million pounds ($514.8 million) at Friday's closing price of 292 pence. Carnival said the strategic reasons for its minority stake in Airtours were "no longer compelling". Airtours said it had agreed to release Carnival from the share lock-up agreement between them. "On the basis that they wanted to pursue their strategy in cruising, we were happy to release them," group chief executive Tim Byrne said. Up to 123.3 million shares will be placed with international institutional investors, with the book expected to close on Thursday.