Stocks in London dipped into the red on Friday morning after data showed an unexpected decline in UK construction output, while utility shares weakened on political uncertainty.The FTSE 100 was down 0.35% at 6,737.10 by midday with SSE and Centrica among the worst performers.Construction output dropped by 2.6% in January after 0.4% growth the month before, surprising analysts who had expected a 1.3% increase. This was the worst fall in over a year.Meanwhile, figures also showed that construction orders were down 2.9% in the fourth quarter of 2014."So there is a very real risk that construction output will contract in the first quarter of 2015 and be a drag on GDP growth, as it was in the fourth quarter of 2014," said economist Howard Archer from IHS Global Insight.The rest of the session is set to be quiet in terms of economic data, with US producer price inflation and consumer confidence figures the only major releases of the day.Utilities weaken, Afren dropsEnergy stocks declined on Friday morning, ahead of the Labour Party conference, during which Ed Miliband is expected to outline plans to cut energy prices if his party wins the General Election. SSE and British Gas owner Centrica were both trading lower.Shares in Afren tumbled after the struggling oil and gas group proposed a debt-for-equity swap with creditors to address its funding needs and recapitalise its capital structure. The company said it "will result in substantial dilution for existing shareholders", and if shareholders don't approve the plan, the company will have no choice but to initiate a sale.Glaxosmithkline edged lower after selling half its stake in former South African associate Aspen Pharmacare for £0.57bn. Having sold 28.2m shares, at a price of 372 rand per share, GSK now holds a 6.2% stake in Aspen, South Africa's largest drug company.JD Wetherspoon served up a slightly short measure of first-half profits as the pubs group saw cost pressures outweigh a rise in revenues. Profits declined 0.9% in the first half while the interim dividend was maintained, causing shares to fall in London.Shares in Premier Inn and Costa owner Whitbread received a boost from UBS which upgraded its rating on the stock from 'sell' to 'neutral' and hiked its target price from 4,700p to 5,400p. Deutsche Bank also lifted its rating on the stock to 'buy'.Spirits group Diageo was shot down by analysts at Credit Suisse as they lowered their recommendation from 'neutral' to 'underperform', saying that the main drivers of earnings growth over the past years each face structural challenges.Market MoverstechMARK 3,175.54 +0.27%FTSE 100 6,737.10 -0.35%FTSE 250 17,088.58 +0.16%FTSE 100 - RisersWhitbread (WTB) 5,375.00p +2.19%British Land Co (BLND) 819.50p +1.80%Meggitt (MGGT) 569.00p +1.70%ARM Holdings (ARM) 1,180.00p +1.55%Coca-Cola HBC AG (CDI) (CCH) 1,123.00p +1.26%ITV (ITV) 252.00p +1.25%Wolseley (WOS) 4,097.00p +1.14%Reckitt Benckiser Group (RB.) 5,775.00p +1.14%GKN (GKN) 366.00p +1.10%Royal Mail (RMG) 430.10p +1.01%FTSE 100 - FallersBG Group (BG.) 819.60p -2.27%SSE (SSE) 1,463.00p -1.88%Centrica (CNA) 236.90p -1.86%Royal Dutch Shell 'B' (RDSB) 2,022.00p -1.51%BHP Billiton (BLT) 1,414.00p -1.50%BP (BP.) 419.55p -1.48%Royal Dutch Shell 'A' (RDSA) 1,933.50p -1.40%Standard Chartered (STAN) 966.00p -1.33%Morrison (Wm) Supermarkets (MRW) 204.90p -1.30%Friends Life Group Limited (FLG) 413.90p -1.29%FTSE 250 - RisersThomas Cook Group (TCG) 156.30p +5.18%Bwin.party Digital Entertainment (BPTY) 83.10p +4.33%Diploma (DPLM) 798.00p +4.25%St. Modwen Properties (SMP) 459.40p +3.94%Allied Minds (ALM) 642.50p +3.71%Home Retail Group (HOME) 180.00p +3.45%Just Eat (JE.) 343.70p +3.34%PayPoint (PAY) 846.00p +3.17%Workspace Group (WKP) 838.00p +3.14%Ocado Group (OCDO) 387.80p +2.84%FTSE 250 - FallersAfren (AFR) 4.80p -26.15%Soco International (SIA) 149.30p -5.86%Cairn Energy (CNE) 152.40p -5.46%Wetherspoon (J.D.) (JDW) 775.00p -4.50%RPS Group (RPS) 230.60p -3.92%Hikma Pharmaceuticals (HIK) 2,263.00p -3.91%Ophir Energy (OPHR) 121.10p -3.35%Vedanta Resources (VED) 512.00p -2.94%Hunting (HTG) 467.90p -2.88%Premier Oil (PMO) 133.50p -2.77%