UK stocks registered decent gains on Monday as markets reacted positively to the withdrawal of Larry Summers from the candidacy to head the Federal Reserve, though investors turned more cautious towards the end of the session.Gains were trimmed slightly in afternoon trade on reports of a shooting at the Navy Yard in Washington DC. A gunman is said to have shot several people and was still on the loose, causing delays to flights from the nearby Reagan International Airport.The FTSE 100 finished 39.06 points higher at 6,622.86, though it ended well below its intraday high of 6,649. Still, this was the best close for London's benchmark index since August 2nd, when it finished the day at 6,647.87.The Stoxx Europe 600 index closed at its highest level since June 2008, Germany's DAX 30 finished at a record, while the S&P 500 in the States was within reach of its all-time high in morning trade.Receding concerns over a potential military attack on Syria also helped markets over the weekend after the US and Russia agreed that Bashar al-Assad's regime must hand over details of its chemical weapons stockpile within a week; the weapons will then be removed and destroyed before mid-2014. Summers pulls out of the runningFormer Treasury Secretary Larry Summers withdrew from the race to replace Ben Bernanke as Fed Chairman when he steps down in January. The removal of well-known hawk Summers prompted a bullish reaction on markets on Monday on the back of hopes that current Fed Vice Chair Janet Yellen - who is expected to favour a slower reduction of stimulus than Summers - could now succeed Bernanke. "Global equities rallied while the 10-year US Treasury yield dropped around 10 basis points and the dollar weakened," said analyst Jessica Hinds from Capital Economic about Summers' withdrawal."This is presumably because Fed Vice Chair Janet Yellen, who is perceived to be more dovish than Summers, now appears the favourite to succeed Ben Bernanke. It may also reflect some relief among investors that the nomination process is likely to be a smoother one."FOMC in focusThe Federal Open Market Committee's two-day meeting is due to come to a close on Wednesday and will likely be one of the most closely-watched policy decisions in recent years, given rising expectations that the Fed will begin to scale back its quantitative easing (QE) programme. According to analysts at Barclays Research, the Fed is likely to taper monthly asset purchases from $85bn to $70bn this week. However, they note that the announcement of tapering by $10-15bn in itself is unlikely to move the market. "We think the key to gauge the market reaction would be: 1) the Fed's updated economic forecasts, especially its forecast for end-2016 to be included for the first time; and 2) the tone in the Chairman Bernanke's press conference regarding the pace/conclusion of tapering," Barclays said. FTSE 100: Fresnillo drops on Mexican levy concernsPrecious metals miners Fresnillo plummeted today on concerns over levies on the mining sector in Mexico. "All of Fresnillo's seven operational mines are in Mexico, leaving it heavily exposed to such an increase in its tax burden," said Financial Sales Trader Max Cohen from Spreadex.Heading the other way were insurers as financials benefitted from the global rally. Standard Life, Legal & General, Aviva and Prudential were among the highest risers, with the latter lifted by Panmure Gordon which raised its target price for the stock saying that the business is "undervalued".Barclays meanwhile was boosted by Nomura which upgraded its rating by two notches from 'reduce' to 'buy' saying that the UK banking group is well-positioned for building macroeconomic momentum. Oil and gas services provider Petrofac was higher on the news that it is to operate and manage two training facilities for Malaysian oil major PETRONAS in a contract worth $120m. Airlines were providing a lift as falling crude prices eased fears about rising jet fuel costs; easyJet and IAG were in demand.FTSE 100 - RisersAntofagasta (ANTO) 883.00p +3.94%Standard Life (SL.) 354.10p +3.33%International Consolidated Airlines Group SA (CDI) (IAG) 325.00p +3.27%Sage Group (SGE) 360.40p +2.77%easyJet (EZJ) 1,331.00p +2.38%Shire Plc (SHP) 2,533.00p +2.26%Aviva (AV.) 419.80p +2.19%Aggreko (AGK) 1,649.00p +2.04%Vedanta Resources (VED) 1,183.00p +1.98%Prudential (PRU) 1,189.00p +1.89%FTSE 100 - FallersFresnillo (FRES) 1,045.00p -12.77%Eurasian Natural Resources Corp. (ENRC) 215.50p -2.05%Rolls-Royce Holdings (RR.) 1,106.00p -1.69%Tate & Lyle (TATE) 786.00p -0.88%Persimmon (PSN) 1,153.00p -0.77%Admiral Group (ADM) 1,214.00p -0.74%ITV (ITV) 182.10p -0.71%GlaxoSmithKline (GSK) 1,614.00p -0.49%Pearson (PSON) 1,277.00p -0.47%Burberry Group (BRBY) 1,602.00p -0.44%FTSE 250 - RisersDunelm Group (DNLM) 997.50p +6.12%Genus (GNS) 1,387.00p +4.76%Xaar (XAR) 798.00p +3.77%PayPoint (PAY) 1,125.00p +3.21%Betfair Group (BET) 1,087.00p +2.94%Beazley (BEZ) 216.40p +2.90%Elementis (ELM) 262.60p +2.70%Fidessa Group (FDSA) 2,173.00p +2.65%Amlin (AML) 400.60p +2.64%Ashtead Group (AHT) 668.50p +2.45%FTSE 250 - FallersHochschild Mining (HOC) 237.40p -13.99%African Barrick Gold (ABG) 143.90p -12.36%Polymetal International (POLY) 659.50p -7.05%Kazakhmys (KAZ) 290.00p -3.69%Petra Diamonds Ltd.(DI) (PDL) 117.40p -2.81%888 Holdings (888) 160.40p -2.79%Cobham (COB) 294.10p -2.39%Halfords Group (HFD) 396.90p -2.24%Atkins (WS) (ATK) 1,212.00p -2.18%TalkTalk Telecom Group (TALK) 252.90p -1.79%BC