The FTSE 100 dipped 0.7% to 7,179 at around 9am as investors digested a raft of corporate news.
Among the biggest fallers were miners and British Gas owner Centrica.
Brent crude oil was stable at $67 per barrel.
MID AND LARGE CAP RISERS
Centrica warned its 2019 financial performance will be impacted by the UK default tariff cap and continuing lower volumes in E&P and nuclear, causing shares in the firm to fall 10.9%.
Financial services firm Standard Chartered was up 0.6% at 620.3p after revealing its fourth quarter results will include a provision of $900m for potential penalties. The penalties are linked previously disclosed investigations.
Defence giant BAE Systems said a German ban on arms exports to Saudi Arabia may hurt its financial performance, prompting a 6.1% fall to 473.6p.
High street bank Barclays rallied 3.5% despite reporting flat pre-tax profits for the full year compared to a year earlier as rising ligation charges weighed on performance. Though the company also more than doubled its total annual dividend to 6.5p
Recruitment group Hays reversed 5.6% despite first half pre-tax profits increasing 8%, driven by net fees growth in its international markets.
Miner Anglo American reported higher annual profits supported rising prices for platinum group metals, but this failed to lift the share price at £20.11.
Public services provider Serco hiked sales guidance for 2019 from a range of £2.8bn to £2.9bn to a range of £2.9bn to £3bn, reflecting recent contract wins. Shares in Serco rose 3.8% to 119.4p.
Go-Ahead Group raised its full year expectations following a better than expected first-half performance in its rail division, helping the stock accelerate 2.5% to £19.64.
Playtech was up 4.5% after announcing its expects 2019 adjusted earnings before interest, tax, depreciation and amortisation to be in the range of €390 to €415m.
SMALL CAP RISERS AND FALLERS
Shares in Purplebricks plummeted 28.3% to 118p after warning on annual sales following slower than expected progress on its second US initiative. The board said revenue for the current financial year is expected to be between £130m and £140m, down from guidance of £165m £175m.