UK stocks fell on Monday, dropping to their lowest in three weeks, as renewed concerns about Greece weighed on sentiment.London's FTSE 100 finished down 0.51% at 6,876.47 by the end of trading on the back of losses in the real estate and construction sectors. The index has not closed below this level since 16 February.Greece's new government has threatened that they could call a referendum or have early elections if the Eurozone rejects its proposed reforms."We are not attached to our posts. If needed, if we encounter implacability, we will resort to the Greek people either through elections or a referendum," said finance minister Yanis Varoufakis.These fears saw Greece's 10-year bond yields rise by a staggering 67 basis points to 10.08% by Monday afternoon.In contrast, yields across the wider Eurozone were lower as the European Central Bank kicked off its landmark bond-buying programme. The bank last week confirmed that its long-awaited scheme to buy up to €1.1tn of government bonds until September 2016 and beyond would start on Monday.In economic data, China's trade surplus rose to a record $60.62bn in February, compared with $60bn in January. This increase came after a 48.3% year-on-year surge in exports and a 20.5% drop in imports, compared with expectations of +14% and -10% respectively.Meanwhile, the German trade surplus shrank to €19.7bn in January from €21.6bn the month before as exports fell 2.1% and imports declined 0.3%.The Sentix Eurozone investor confidence index rose to a seven-year high of 18.6 in March, up from 12.4 in February and ahead of the 15 consensus estimate.Real estate and CRH provide a dragProperty stocks including Land Securities, British Land and St Modwen Properties were out of favour on Monday as gilt yields rose. Higher yields on low-risk UK bonds typically reduce the attractiveness of income stocks such as those in the real estate sector.Increased speculation about an earlier-than-anticipated rate rise by the Federal Reserve after last week's strong US jobs report also dampened the share price of building materials group CRH, which is heavily exposed to the American economy. On 6 March the yield differential on 10-year Gilts versus their German equivalent reached its greatest level since 1997 on the heels of a strong US jobs report.CRH was also likely weighed down by new hurdles in the proposed merger between Holcim and Lafarge - CRH's planned acquisition of €6.5bn of assets from the two cement giants is conditional on their tie-up completing.Standard Chartered gained after Exane BNP Paribas raised its target price on the stock and amid speculation that the company could move its global headquarters.However, others in the banking sector such as Lloyds, RBS, Barclays and HSBC were trading in the red. The latter was the object of negative coverage in the FT Weekend.WPP, the world's biggest advertising company, rose after beating expectations with a record £1.5bn annual profit in 2014, up 12% on the previous year. Revenues were up nearly 5% at £11.6bn, though currency movements weighed on growth.Market MoverstechMARK 3,149.39 -0.55%FTSE 100 6,876.47 -0.51%FTSE 250 17,167.07 -0.61%FTSE 100 - RisersWeir Group (WEIR) 1,887.00p +4.08%Glencore (GLEN) 296.90p +2.56%Standard Chartered (STAN) 1,044.00p +1.95%easyJet (EZJ) 1,702.00p +1.31%Legal & General Group (LGEN) 283.90p +1.18%WPP (WPP) 1,559.00p +1.17%Morrison (Wm) Supermarkets (MRW) 208.20p +1.07%Smiths Group (SMIN) 1,191.00p +1.02%Rolls-Royce Holdings (RR.) 995.50p +0.86%Centrica (CNA) 243.90p +0.79%FTSE 100 - FallersCRH (CRH) 1,727.00p -3.90%Experian (EXPN) 1,160.00p -2.27%Royal Bank of Scotland Group (RBS) 367.80p -2.21%Land Securities Group (LAND) 1,239.00p -2.06%Travis Perkins (TPK) 1,969.00p -2.04%Tullow Oil (TLW) 346.10p -2.01%Schroders (SDR) 3,090.00p -1.94%Associated British Foods (ABF) 3,069.00p -1.92%Aggreko (AGK) 1,568.00p -1.88%British American Tobacco (BATS) 3,756.00p -1.82%FTSE 250 - RisersGame Digital (GMD) 274.90p +5.33%Betfair Group (BET) 2,156.00p +4.36%Jardine Lloyd Thompson Group (JLT) 993.00p +3.55%NMC Health (NMC) 630.00p +2.86%Spire Healthcare Group (SPI) 334.00p +2.77%Ocado Group (OCDO) 370.50p +2.63%Entertainment One Limited (ETO) 292.60p +2.56%Synthomer (SYNT) 294.00p +2.44%National Express Group (NEX) 285.80p +2.04%Hunting (HTG) 507.50p +1.97%FTSE 250 - FallersAfren (AFR) 5.47p -8.07%Polymetal International (POLY) 522.50p -4.13%Big Yellow Group (BYG) 620.00p -3.95%Centamin (DI) (CEY) 57.45p -3.69%Lonmin (LMI) 126.30p -3.44%Tullett Prebon (TLPR) 365.00p -3.18%St. Modwen Properties (SMP) 449.00p -3.00%BBA Aviation (BBA) 334.90p -2.93%Hikma Pharmaceuticals (HIK) 2,331.00p -2.71%Home Retail Group (HOME) 197.70p -2.71%