FTSE 100 slips back on renewed US 'cliff' worries Investor optimism over the state of the US economy proved short-lived, with concerns over the "fiscal cliff" weighing on London's blue-chips a day after the Federal Reserve met market expectations by boosting stimulus measures. The FTSE 100 slipped 15 points this morning after gaining 20.88 points on Wednesday when traders bet that Ben Bernanke, the Fed chairman, would expand quantitative easing. While the central bank yesterday announced a further $45bn (£28bn) of monthly government bond repurchases after markets in London closed, Mr Bernanke warned that the Fed could not avert the impact of looming tax increases and spending cuts, the so-called "fiscal cliff" that is due to kick-in next year unless politicians can negotiate a compromise. The cliff threatens to plunge the US into recession. Among individual stocks on the blue-chip index, AstraZeneca was a heavy faller after revealing disappointing clinical test results for its experimental arthritis drug Fostamatinib. The shares fell 2.3pc in early deals. On the mid-cap FTSE 250, which slid 24 points this morning, Egyptian gold miner Centamin plunged 41pc on the news the company was suspending operations at its Sukari mine, its main asset, following a dispute over fuel and problems with gold exports. The group's operations in Egypt came under threat earlier this year after a court ruled its right to dig at Centamin was invalid, a judgement the company is appealing. "It appears to be suffering a run of very bad news, which highlights the difficulties of operating in Egypt, where the political environment remains volatile," said analysts at Investec. We do question, however, how well political issues are being managed by Centamin and how long they fester before reaching a critical point.