Weaker commodity prices weighed on miners and oil majors, dragging the FTSE 100 lower by 0.5% to 7,228 around midday.
BP (BP.) slid 1.6% to 496.1p and Royal Dutch Shell (RDSB) lost 0.9% to £24.10.
The wane in oil prices followed a dialling down of tensions over the geo-political situation in Syria. Brent crude oil fell 1.2% to $71.72 per barrel.
Miner Fresnillo (FRES) declined 1.5% to £12.65 and Randgold Resources (RRS) retreated 1.1% to £57.20.
MID AND LARGE CAP RISERS AND FALLERS
Shares in Costa Coffee and Premier Inn owner Whitbread (WTB) frothed 6.7% higher to £41.97 after activist investor Elliott Advisors became the largest investor in the company. According to reports, Elliott is seeking a spin-off of Costa.
Advertising colossus WPP (WPP) fell 6.1% to £11.15 as investors reacted to the resignation of chief executive Martin Sorrell, who had been subject to a misconduct probe.
Rare diseases specialist Shire (SHP) was up 1.3% at £36.53 after agreeing to sell its oncology business to French rival Servier for $2.4bn amid a potential takeover approach from Takeda.
Polymetal (POLY) announced it will receive 85% of copper-gold East Tarutin deposit licence holder Tarutinskoye in return for 100% of Polymetal's licence holder Vostochny Basis of the copper-gold Tarutin deposit. Its shares dropped 6.7% to 630.4p.
SMALL CAP RISERS AND FALLERS
Orosur Mining (OMI) revealed lower production in its third quarter following a change in approach to its Uruguay gold project, dragging the shares 13.4% lower to 5.5p.