Vodafone's volatile stock has cost it its position as Europe's leading company and allowed BP to take over at the top of the FTSE-100 index.The mobile giant's shares dipped below £2 for the first time since January 1999 at 12:00 (GMT) today, trading at 195.5p or down 4.2 per cent on its opening price. This meant BP Amoco, which was overtaken by Vodafone in January 2000, moved into pole position. The oil firm, valued on the London Stock Exchange at £128.9bn, is now worth more than Vodafone, whose value has dipped to £126.3bn. Vodafone became the most valuable company in Europe when it purchased German rival Mannesmann in March 2000 in a £115bn deal. However, its shares have more than halved since it peaked at 399p on 6 March last year. The fall comes hard on the heels of news that Italian anti-trust authorities might place conditions on Vodafone's sale of Infostrada to Italy's state-controlled electricity company Enel.