After a positive open, the FTSE 100 sank into the red in early trade, falling over half a percent to 8,704 in the first half hour.
Melrose Industries is down 5% despite results that looked ahead of expectations.
HSBC Holdings is down 3.4% as its shares go ex-dividend, along with Rio Tinto, Berkeley Group and LondonMetric Property.
Rentokil and Reckitt Benckiser are also trading lower following the release of their latest financials.
On the upside, Admiral Group is top of the FTSE 100 leaderboard after the insurer reported profits ahead of forecasts, even though it said "the market is softening and the outlook is uncertain".