Amid another day of market turmoil, which saw the FTSE 100 fall by 2.5 per cent, investors in BG Group found some comfort as the petrochemicals company rose on bid talk.

Speculation in the Square Mile suggested that the company could find itself the subject of a takeover approach from ExxonMobil, the American energy giant.

The British company, which specialises in natural gas, is trying to push through a A$13.8 billion (£6.4 billion) hostile takeover of Origin Energy, of Australia, and is increasingly being seen as a key energy asset for the future – given its involvement in potentially huge oilfields off the coast of Brazil.

This is not the first time that BG has been subject to bid speculation, with the likes of Royal Dutch Shell, Gazprom, the Russian gas giant, and state-owned Petrobras, of Brazil, all seen as potential predators in the past.

BG also received a boost from analysts at MF Global, which upgraded the stock to “buy”, from “neutral”, saying that its recent share price weakness represented an attractive buying opportunity. The shares rose by 8p to £10.55, with nearly 20 million shares traded, almost double the normal number, but the company refused to comment on market speculation.

The FTSE 100 index dived for the second day in succession, falling by 137.6 points to 5,362.1 as data from across the Atlantic and growth warnings from Europe hit blue-chip stocks. Figures from Halifax, the home-loan provider, showing that house prices in the UK fell by 10.9 per cent in August also weighed on the index.

The biggest shock to the market was that US unemployment rose towards a five-year high last week, as employers cut staff in the face of a weakening global economy.

The European Central Bank cut its projections for economic growth in the eurozone for this year and next. It also unveiled plans to tighten criteria for certain loans to commercial banks, in response to concern that its lending facilities were being misused by banks putting up questionable assets as collateral. Both the ECB and the Bank of England left interest rates unchanged as expected.

Banks were worst hit, with HBOS down 20¾p at 282½p, Barclays falling 21p to 329¼p and Lloyds TSB 17¼p lower at 286¼p.

Retailers, such as Marks & Spencer, down 14p at 247p, and Tesco, 10.9p lower at 377.1p, also suffered.

Concerns about the global economy hit metal prices, with Ferrexpo down 13¼p to 198p and Anglo American losing 129p at £24.30.

Unilever led the index, up 91p to £15.81, as investors welcomed the appointment of Paul Polman, head of Nestlé’s Americas division, as its next chief executive.

BAE Systems fell 21¼p to 464p, although it could rise this morning after it emerged that it is in talks with Westinghouse, which will allow it to enter the civil nuclear market.

Cadbury made ground, rising 5p to 622p, after Lehman Brothers raised its target price on the stock to 800p, citing its resilient portfolio and noting that it was a takeover candidate.

— New York: Wall Street stocks tumbled following disappointing economic news and sluggish results from retailers. The Dow Jones industrial average closed down 344.6 points at 11,188.20.

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