Investors are betting that a juicier bid for Shire could be in the works, after the pharmaceutical company won a key patent ruling in the US.
A judge upheld Shire's claim that generic drug makers are infringing on patents relating to Shire's best-selling hyperactivity drug Vyvans.
Mick Cooper, analyst at Edison Investment Research, said the ruling "strengthened Shire's hand" in its fight against AbbVie's takeover bid, launched last week. The speculation helped Shire climb 113p to 4,517p.
It was one of the few companies to make gains as the sell-off on the bluechip index accelerated. Uncertainty in Iraq and a downward revision of US first quarter GDP figures turned investors off equities and the FTSE 100 slipped to its lowest level since April, down 53.45 points at 6,733.62.
Meggitt was the worst performer, falling 17p to 508.5p after a downgrade from JPMorgan.
Premier Oil retreated 13.8p to 322.1p on the mid-cap index as the independent fossil fuel specialist named finance director Tony Durrant as successor to out-going chief executive Simon Lockett.
City stalwart and Tullet Prebon chief executive Terry Smith's new investment vehicle Fundsmith Emerging Equities Trust got off to a strong start as a listed company, closing at 1,040p on its first day of trading after being offered at 1,000p.
Recently floated Card Factory received a trio of analyst endorsements, as UBS, Investec and Nomura all gave it a buy rating. But after a strong morning rally, the company ended the day up just 1.5p at 206p.
Quindell chairman Rob Terry upped his stake in the AIM-listed insurance outsourcing business, which recently missed out on a premium listing. It crept up 7.5p to 209p.
Sheffield headquartered Synectics tumbled 97p to 329p after a profit warning. The company blamed the crisis in Iraq for knocking off £7m its revenue forecast and £2.1m from predicted net profit.
Hydrogen energy group Acta also lost 0.75p to 4.12p after warning that revenue for the year could be "below current market expectations".