London stocks advanced on Wednesday morning, rising for a third straight day, as investors took a bullish approach ahead of the hotly-anticipated UK Budget and Federal Reserve policy decision.The FTSE 100 was trading up 0.3% at 6,859.81 in early deals.The market reaction to chancellor George Osborne's Budget statement, due at 12:30, is expected to be only small, though it will give a chance to see where the Conservatives are placed ahead of the General Election in May.Nevertheless, investors will be watching oil stocks on speculation that tax breaks for North Sea producers may be announced, while housebuilders will likely be looking out for potential stimulus measures in the housing market.As for the Federal Open Market Committee meeting (18:00), no change is expected in the policy stance though forward guidance will be in focus given recent speculation that policymakers will drop the term 'patient' when referring to the first rate hike."We expect the key sentence that the Fed can afford to be 'patient' in normalising monetary policy to be removed from the statement. This will not signal an imminent hike but underscore that a rate hike is now on the agenda but timing will be data dependent," said analysts at Danske Bank.Also on the agenda for Wednesday's session will be data on UK employment, Bank of England minutes, US mortgage applications and US crude inventories.StanChart boosted by upgradeShares in emerging markets-focused bank Standard Chartered surged after Barclays upgraded its rating on the stock from 'equal weight' to 'overweight' and lifted its target price from 1,000p to 1,150p. Analysts said that the appointment of a new chief executive "mark[s] a turning point".At the same time, Barclays cut its recommendation on HSBC from 'overweight' to equal weight' due to "a combination of higher capital requirements, macro headwinds and the need for further significant restructuring". HSBC shares were trading broadly flat early on.Housebuilders were making decent gains, such as Taylor Wimpey, Barratt Developments and Persimmon. "Housebuilding shares could also get a boost if we get investment initiatives to build more properties, given the pressure on housing," according to analyst Michael Hewson from CMC Markets.Pharmaceutical giant AstraZeneca gained after reporting that Phase III studies into investigative drug PT003 for chronic lung disease had delivered positive results.Oil and gas outfit BG Group fell despite the announcement of first oil from its part-owned Knarr field in the North Sea offshore Norway. BG, along with a number of energy stocks such as Tullow Oil and Centrica, were pulling back after strong gains on Tuesday.Mining stocks were also retreating after solid gains, with Fresnillo, Antofagasta, Rio Tinto, Anglo American and Glencore all in the red. Antofagasta in particular was feeling the effects of a downgrade by Beaufort Securities to 'hold'.Smiths Group fell after first-half underlying profits at the engineering company stumbled 3% on the hurdles of foreign currency and the lower oil price.Market MoverstechMARK 3,225.77 +0.26%FTSE 100 6,859.81 +0.32%FTSE 250 17,250.30 +0.28%FTSE 100 - RisersStandard Chartered (STAN) 1,023.50p +6.06%CRH (CRH) 1,720.00p +1.96%Marks & Spencer Group (MKS) 513.50p +1.68%Taylor Wimpey (TW.) 151.30p +1.34%Travis Perkins (TPK) 1,975.00p +1.28%Reed Elsevier (REL) 1,161.00p +0.96%Prudential (PRU) 1,714.00p +0.94%AstraZeneca (AZN) 4,683.50p +0.94%Direct Line Insurance Group (DLG) 324.30p +0.87%Barratt Developments (BDEV) 526.50p +0.86%FTSE 100 - FallersFresnillo (FRES) 637.50p -3.26%Weir Group (WEIR) 1,743.00p -2.08%Tullow Oil (TLW) 292.80p -1.88%Rio Tinto (RIO) 2,840.00p -1.17%Randgold Resources Ltd. (RRS) 4,621.00p -1.09%Anglo American (AAL) 1,060.00p -1.07%Antofagasta (ANTO) 680.00p -1.02%Glencore (GLEN) 280.15p -0.78%Burberry Group (BRBY) 1,856.00p -0.75%Lloyds Banking Group (LLOY) 78.97p -0.62%FTSE 250 - RisersEuromoney Institutional Investor (ERM) 1,053.00p +2.93%Allied Minds (ALM) 647.00p +2.21%Savills (SVS) 758.00p +2.16%Morgan Advanced Materials (MGAM) 338.80p +2.02%Spire Healthcare Group (SPI) 361.60p +1.95%Synthomer (SYNT) 296.50p +1.75%NMC Health (NMC) 654.50p +1.71%Countrywide (CWD) 529.50p +1.63%IP Group (IPO) 236.00p +1.59%Essentra (ESNT) 1,012.00p +1.56%FTSE 250 - FallersAfren (AFR) 2.92p -9.06%Just Eat (JE.) 347.70p -4.74%Vedanta Resources (VED) 425.20p -3.93%Premier Oil (PMO) 136.30p -3.26%esure Group (ESUR) 219.40p -3.05%Saga (SAGA) 173.10p -2.70%Phoenix Group Holdings (DI) (PHNX) 841.50p -1.92%Cairn Energy (CNE) 151.40p -1.62%AL Noor Hospitals Group (ANH) 997.00p -1.58%Hunting (HTG) 466.60p -1.54%