* Uncertainty around Brexit and stimulus keeps investors sidelined * ECB expected to expand and extend stimulus * Uncertainly remains over U.S. stimulus LONDON, Dec 10 (Reuters) - Bets on more European Central Bank stimulus kept Europe’s main stock markets and the euro steady on Thursday, but Britain’s pound saw its biggest drop in almost a month after overnight Brexit talks turned sour. It had been a mixed session for Asia amid a surge in coronavirus cases and the ejection of some Chinese stocks from S&P Dow Jones’ indices, so there was little surprise when Europe struggled to add to recent highs. The pan-European STOXX 600 index was flat, though London’s FTSE 100 did score its eighth straight gain as the Brexit uncertainty pushed the pound down 0.8% to just under $1.33 and 90.95 pence per euro. European Union and British leaders gave themselves until the end of the weekend to seal a new trade pact, with some $1 trillion in annual trade at risk of tariffs if they can’t reach a deal by Dec. 31, when transition arrangements end. “There’s still clearly some scope to keep talking, but there are significant points of difference that remain,” Foreign Secretary Dominic Raab told BBC TV. “(On) Sunday, they need to take stock and decide on the future of negotiations.” For the ECB, economists expect its 1.35 trillion-euro PEPP stimulus plan to be expanded by at least 500 billion euros and its duration extended by six months to the end of 2022, with risks skewed towards even more. The bank will announce its policy decision at 1245 GMT, followed by ECB chief Christine Lagarde’s 1330 GMT news conference. Traders will be also listening to what she says about the euro’s near 14% rise since March. “The critical element is that there has been an impact on (euro zone) growth recently,” said Shoqat Bunglawala, head of global portfolio solutions for EMEA & APAC at Goldman Sachs Asset Management, referring to the second wave of lockdowns. “So we would expect to see some further support.” Euro zone government bond yields - which move inversely to price - continued to fall. Italian 10-year yields fell to a record low at 0.53%. Spain and Portugal’s hit 0.013% and -0.022% respectively. In Asian trading, MSCI’s broadest index for the region eased 0.4%, with Japan’s Nikkei ending 0.2% lower. Both are up more than 60% from March lows. S&P 500 futures were holding 0.1% higher, however, after the Nasdaq dropped 2% on Wednesday, when U.S. regulators filed lawsuits against Facebook alleging the company used its dominance to buy or crush rivals, harming competition.