Troubled construction services company Carillion (CLLN.L), which has seen 70 percent of its market value wiped out since a profit warning and the exit of its CEO on Monday, slipped another 3.1 percent in choppy trading as JPMorgan slashed its "overweight" rating to "neutral".
Investors shunned AstraZeneca (AZN.L) shares, which slid 3.4 percent to the bottom of the FTSE after a media report said Chief Executive Pascal Soriot could be preparing to defect to Israel-based Teva Pharmaceutical Industries (TEVA.TA). The company declined to deny the report.
Some analysts questioned whether reports of a move suggested the results of the company's MYSTIC trial of a lung cancer candidate could fail - although others said they saw no link.
"We find it hard to believe a Soriot departure would have direct read-across to (key lung cancer trial) Mystic, and would favour remuneration and the UK mood music as at least a key part of the explanation," said Liberum analyst Roger Franklin.
"Any significant fall today could therefore be a buying opportunity for long-term investors," he added.
BT led blue-chip gainers and Europe's telecoms sector .SXKP, up 4 percent after UK broker Numis started covering the company with a "buy" rating.
"Earlier this year the company and (regulator) Ofcom gave many BT shareholders much heartache, but at current levels we believe the share price discounts some incredible assumptions," Numis analysts wrote.
Retailers Marks & Spencer (MKS.L) and Next (NXT.L) made solid gains, as investors read across from stronger results reported by French supermarket Casino (CASP.PA), lifting retailers across Europe .SXRP.
N Brown (BWNG.L) slid 6.5 percent, the worst mid-cap faller, after the plus-size fashion retailer said it would incur an exceptional charge of up to 40 million pounds ($52 million) for potential customer redress on flaws in products sold between 2006 and 2014.
Ocado (OCDO.L) gained 2.4 percent, however, after Credit Suisse raised its target price on the stock, predicting the online grocer would expand margins through automation.
"Whereas we think the market has tended to view Ocado's latest-generation facility as the endpoint of the investment case, we believe this platform will allow Ocado to drive widespread automation and monetise its intellectual property," analysts at the Swiss bank wrote.
Barclays said fears of the impact on housebuilders from potential interest rate rises were "overblown", upping its ratings on some firms.
Reporting by Helen Reid and Kit Rees; Editing by Alison Williams