Banking shares are dragging London's top stocks lower in early dealings on Friday, after President Obama revealed tough new measures to curb risk-taking among the big Wall Street banks. Obama proposed rules to limit bank mergers and consolidation, while also restricting involvement in hedge funds, private equity activity and proprietary trading. The Dow Jones plunged more than 200 points as a result.Over here, Royal Bank of Scotland, Barclays and Lloyds Banking are all among the main fallers.Resource stocks, at least, had some early good news for investors, with miner Xstrata and oil company Tullow giving updates on their activities. Xstrata's copper division has upgraded a mineral resource estimate for its Horse-Ivaal-Trukai deposit at the Frieda River copper-gold project in Papua New Guinea. The mining giant, which assumed management control of the project two years ago, said the new resource estimate includes 'significantly' increased inventory and improved confidence levels, including a 26% increase in resource tonnage.Tullow Oil said its Kasamene-2 appraisal well, which is located in the Butiaba region of Uganda Block 2, has encountered 39 metres of net oil pay and 8 metres of net gas pay within a 132 metre gross interval. Defence and aerospace group Cobham has named National Express chairman John Devaney as chairman designate of the company. Devaney will succeed David Turner as chairman in May, by which time he will have given up his executive responsibilities at National Express.Engineer Invensys said it still expects to achieve an improvement in performance in the current year. Invensys said operating profit before exceptional items in the third quarter was ahead of the corresponding period last year despite the continuing difficult economic climate. The group was behind 2008 levels at the halfway point at the end of September.Acquisitive electronic sensors company Halma has beefed up its presence in the photonics market through the purchase of SphereOptics, a US manufacturer of precision products for use in light metrology applications. The company is initially paying $2.5m (£1.5m) for the New Hampshire based company. SphereOptics had revenues of $4.3m (£2.6m) in 2009.Merchant bank Close Brothers said it remains confident that it will deliver a good overall result for the first half and a solid outcome for the full year, but cautioned that this will depend on the prevailing economic environment and financial market conditions.Transport and logistics group Stobart is confident that it will meet its year end pre-tax profit expectations and deliver further value from its substantial asset base. Dragon Oil aims for stronger growth in 2010 after putting eight wells into production last year and anticipating completion of 11 wells over the next 12 months.Diamond prices continued their 'impressive' recovery in the fourth quarter, though they still lag behind 2008 levels, Gem Diamonds boss Clifford Elphick said.Household goods and engineering group Metalrax expects its performance pre exceptional items for the full year ended December to be slightly ahead of market forecasts.FTSE 100 - RisersTullow Oil (TLW) 1,300.00p +1.72%National Grid (NG.) 654.00p +1.40%United Utilities Group (UU.) 532.00p +1.33%Severn Trent (SVT) 1,157.00p +0.87%Kingfisher (KGF) 225.00p +0.76%Marks & Spencer Group (MKS) 352.50p +0.60%Burberry Group (BRBY) 615.00p +0.57%Resolution (RSL) 83.95p +0.54%Invensys (ISYS) 305.00p +0.53%Pearson (PSON) 896.00p +0.50%FTSE 100 - FallersRoyal Bank of Scotland Group (RBS) 33.58p -4.93%Barclays (BARC) 270.70p -4.35%ICAP (IAP) 411.30p -3.38%Kazakhmys (KAZ) 1,246.00p -2.66%Lloyds Banking Group (LLOY) 52.30p -1.88%London Stock Exchange Group (LSE) 683.00p -1.66%Fresnillo (FRES) 716.00p -1.65%Xstrata (XTA) 1,082.00p -1.55%Randgold Resources (RRS) 4,617.00p -1.49%Home Retail Group (HOME) 258.30p -1.45%