- Annual UK GDP growth revised higher- Ukraine crisis in focus as Russian convoy nears border- BHP leads miners higher on demerger commentstechMARK 2,763.55 +0.51%FTSE 100 6,726.15 +0.61%FTSE 250 15,757.92 +0.53%London stocks advanced on Friday after an upgrade to UK second-quarter growth estimates and a jump in the share price of mining giant BHP Billiton.BHP was leading gains in the heavyweight resources sector in morning trade after saying that it considering the demerger of certain non-core businesses.The Office for National Statistics' second estimate of annual UK gross domestic product (GDP) growth in the April-to-June period was lifted unexpectedly to 3.2%. This was up 10 basis points from the original prediction on the back of a strong construction sector and marked the strongest annual growth rate in over six years. The estimate for quarter-on-quarter growth of 0.8% was left unchanged.The FTSE 100 was up 0.6% at 6,726 by midday, heading for a weekly gain of around 2.5%. The last time the Footsie closed higher was on 31 July when it settled at 6,730.11.Disappointing indicators from China and a stagnation in Europe has spurred hopes in recent days that policymakers will step in to give growth a boost. Easing concerns about an early rate hike by the Bank of England were also supporting stocks after the central bank warned about weak wage growth in the UK.Comments on Thursday from Russian President Vladimir Putin about ending the crisis in Ukraine were also helping investor risk appetite in London, as well as the resignation of Iraq Prime Minister Nouri Maliki overnight as he supported the formation of a new government.However, markets were keeping a close eye on developments in Ukraine due to reports of armoured personnel vehicles crossing the border from Russia amid an ongoing row over Moscow sending a convoy of humanitarian aid.Friday afternoon will see the release of a host of US economic data, including the producer price index, Empire State manufacturing, industrial production and University of Michigan consumer confidence.BHP gains on demerger commentsBHP Billiton shares were up 2.2% after the miner said that it is considering a demerger of certain assets in an effort to make the business "simpler and more productive". The company, reiterated its focus on its "four pillars" - iron ore, copper, coal and petroleum - with potash being a potential fifth, suggesting that nickel, aluminium and bauxite assets could be spun off. It will update the market after the board reconvenes next week.Other miners such as Rio Tinto, Anglo American and Glencore were also performing well.Shares in Smith & Nephew were under pressure after analysts at Morgan Stanley downgraded the medical devices maker from 'overweight' to 'equal weight'. The bank said that even if US peer Stryker returns with a bid in November, the deal "remains uncertain" and the stock "could start to lose its M&A premium of around 10%" in the near term.Construction group Balfour Beatty edged higher after reaffirming its rejection of a takeover proposal by Carillion, branding it "opportunistic" and accusing Carillion of wanting to reduce Balfour's UK construction revenues by up to two-thirds. Carillion's shares were firmly lower in morning trade.FTSE 100 - RisersBHP Billiton (BLT) 2,070.50p +2.22%Ashtead Group (AHT) 912.00p +1.96%Tesco (TSCO) 249.85p +1.90%Sports Direct International (SPD) 701.50p +1.81%Imperial Tobacco Group (IMT) 2,546.00p +1.72%3i Group (III) 376.80p +1.65%Smiths Group (SMIN) 1,275.00p +1.59%Babcock International Group (BAB) 1,109.00p +1.46%Barratt Developments (BDEV) 356.10p +1.42%Experian (EXPN) 1,036.00p +1.37%FTSE 100 - FallersRoyal Mail (RMG) 439.90p -0.83%Petrofac Ltd. (PFC) 1,136.00p -0.70%easyJet (EZJ) 1,281.00p -0.62%G4S (GFS) 265.00p -0.60%Fresnillo (FRES) 1,021.00p -0.58%HSBC Holdings (HSBA) 647.70p -0.57%Aviva (AV.) 504.50p -0.30%Smith & Nephew (SN.) 1,038.00p -0.29%Shire Plc (SHP) 4,841.00p -0.25%Aggreko (AGK) 1,716.00p -0.23%FTSE 250 - RisersAfren (AFR) 101.50p +4.21%Premier Oil (PMO) 338.40p +3.64%Ocado Group (OCDO) 348.60p +3.60%Genus (GNS) 1,102.00p +3.28%Big Yellow Group (BYG) 539.50p +2.96%Tullett Prebon (TLPR) 280.40p +2.82%JD Sports Fashion (JD.) 407.00p +2.31%EnQuest (ENQ) 122.20p +2.26%Redrow (RDW) 257.30p +2.22%Computacenter (CCC) 624.00p +2.21%FTSE 250 - FallersJust Eat (JE.) 247.80p -5.42%SVG Capital (SVI) 410.70p -4.38%Exova Group (EXO) 219.40p -4.19%Millennium & Copthorne Hotels (MLC) 585.50p -2.82%Fidessa Group (FDSA) 2,222.00p -2.59%Carillion (CLLN) 338.30p -2.45%Centamin (DI) (CEY) 68.45p -2.07%Spirent Communications (SPT) 101.30p -1.94%Xaar (XAR) 576.00p -1.87%Hochschild Mining (HOC) 166.00p -1.78%BC