But concerns over US military action against Syria sent the wider FTSE-100 Index into the red, down 51.13 points, or 0.79%, to 6440.97, adding to investor caution over the timing of America's plans to taper its quantitative easing drive.
Markets have been rattled by developments in Syria, with US Secretary of State John Kerry suggesting the administration is edging closer to a military response following "undeniable" evidence of a large-scale chemical weapons attack.
Growing fears over military intervention have sent oil prices up, with the benchmark New York rate rising 2.81 US dollars a barrel to 108.73 dollars.
In currency markets, the pound weakened ahead of new Bank of England governor Mark Carney's speech today amid expectations he will look to rein in the recent hike in UK money market rates and reiterate a pledge to keep interest rates at their current record low of 0.5%. Sterling fell 0.3% to 1.55 dollars and 0.4% to 1.16 euros.
The Middle East uncertainty was reflected in the performance of British Airways owner International Airlines Group, which fell 15.3p to 300.5p.
M&S shares were boosted after Citigroup backed the retailer's prospects following a long period in the doldrums.
In a boost for chief executive Marc Bolland, Citigroup upgraded the FTSE-100 stock to buy from neutral and raised its price target to 535p from 470p, citing improved economic conditions and faith in management turnaround plans.
M&S was among the leading risers, up 2% or 7.5p to 479.1p, in a session when rival Next was 74p higher at 4990p after Bank of America Merrill Lynch raised its rating from neutral to buy and said its research showed that the retailer had been more price competitive in recent weeks.
Shares in security group G4S lost early session gains - closing down 0.5p to 245.3p - on the eve of half-year results, when new chief executive Ashley Almanza is expected to outline plans for a radical overhaul of the troubled business.
There has also been speculation that Cevian Capital, an activist investor, is planning to double its stake in G4S to 10%.
Meanwhile, shares in TalkSport owner UTV Media were under pressure - down 7p to 167p - after its half-year profits fell 43% to £6.1 million.
The biggest FTSE-100 risers were Petrofac up 108p to 1373p, Fresnillo ahead 87p to 1310p, Randgold Resources 210p higher at 5335p and BG Group 28p up at 1210p.
The biggest FTSE 100 fallers were International Airlines Group down 15.3p to 300.5p, GKN off 14.7p to 331.4p, Royal Bank of Scotland 14.2p lower at 330.1p and Aberdeen Asset Management down 14.7p to 352p.