Britain's top share index fell 0.8 percent early on Monday, as energy producers and miners were dragged lower by falling commodity prices, but Anglo American gained as Xstrata proposes merger talks.
By 0802 GMT the FTSE 100 was down 33.77 points at 4,312.16 after gaining 1.5 percent to close at 4,345.93 on Friday.
Anglo American was the biggest blue-chip gainer, up 9.4 percent after rival Xstrata said it wanted talks about a proposed merger of equals, worth about $68 billion seeking increased scale and cost synergies.
Xstrata fell 1.8 percent, and Lonmin slipped 2.6 percent as investors speculated that Xstrata could sell its 24.9 percent stake in the miner as the result of the merger. Other miners fell in the face of weaker metal prices. Rio Tinto, Kazakhmys, Eurasian Natural Resources, and BHP Billiton were all in negative territory.
Energy firms were weaker as oil fell towards $69 per barrel as bearish sentiment over gasoline markets in the U.S. dominated the mood of investors.
BP, Royal Dutch Shell, BG Group, Tullow Oil and Cairn Energy fell between 1.7 and 2.7 percent.
"Oil prices were off slightly, hurting energy stocks and there's some weakness in banks," said Richard Hunter, head of equities at Hargreaves Lansdown.
"Now as we come into the summer period in the absence of any positive news, we are likely to trend sideways."
The FTSE 100 is up 24.4 percent since touching a six-year trough in early March but it is still down 2.9 percent on the year.
Emphasising the bleak economic backdrop, asking prices for homes in most of Britain fell in June after four months of rises, property website Rightmove said on Monday.
Average asking prices of properties new to the market fell 0.4 percent this month, after rising 2.4 percent in May, Rightmove said. The annual rate of decline eased to 5.5 percent, its lowest since last October, from 6.2 percent in May.
Banks were broadly weaker: Barclays, HSBC, Standard Chartered, and Lloyds Banking Group fell 0.1 to 2.7 percent but Royal Bank of Scotland bucked the trend, adding 1.1 percent.
Drugmakers also fell, retreating from some gains made last week. GlaxoSmithkline fell 0.8 percent and and AstraZeneca fell 1.3 percent.
There is little in the way of major economic data coming out of the UK this week so the main macro focus will be across the Atlantic, most notably on the latest two-day Federal Reserve Open Market Committee meeting which begins on Tuesday.
With interest rates at rock-bottom, no changes are anticipated from the Fed, though any comments on the progress of quantitative easing moves and signs of recovery in the economy would be welcomed by the market.
The FTSE 100 index had a slightly different make-up on Monday as the latest quarterly reshuffle took effect, with London Stock Exchange, 3i Group, and Wolseley all making a return to blue chip status after one quarter in the mid caps.
