The retailer closed 7% lower, while BAE Systems also lost 7% as excitement over Wednesday's news of mega-merger talks with Airbus owner EADS turned to fears over the potential hurdles.
The wider FTSE-100 index closed 37.8 points higher at 5819.9 amid hopes US policy-makers would unveil a new round of emergency support.
That optimism proved well founded as after the London market closed the US Federal Reserve confirmed more quantitative easing for the world's biggest economy.
The Fed intends to buy $40 bil-lion (£24.8bn) of securities a month for an open-ended period until the job market improves and promised to keep interest rates at rock bottom until at least the middle of 2015.
JJB Sports had a rollercoaster day, with its share price almost doubling in early trading before a late afternoon slump when the retailer confirmed it had received bids to buy the company but any deal would lead to shareholders seeing their stakes wiped out. It finished the day up 0.1p at 0.45p.
Next's ominous trading warning put the group firmly in the spotlight and overshadowed news of a 10% jump in first-half profits to £251 million.
The group said recent trading had been disappointing following an "unusually quiet" August and September, sending shares down 259p to £33.20.
Shares in BAE Systems were also at the bottom of the Footsie index after the group confirmed talks over a potential merger with Airbus aircraft manufacturer EADS.
The statement triggered a 11% surge in the share price, but the stock slipped 26.5p to 337.1p amid fears over the political, regulatory and business hurdles the merger may face.
However, chipmaker ARM Holdings made gains after Apple impressed investors with the iPhone 5, which uses ARM technology. ARM's shares were 7p ahead at 562p.
Telecoms giant BT was 1% higher as households discovered the group is to hike its prices from January 5 next year, with phone calls, line rental and broadband rising by up to 5.9%.
The price revelations came after BT agreed to pay £738m for the rights to 38 Premier League football matches a season for three years amid fears it vastly overpaid. The shares were 1.6p higher at 236.8p.