UK stocks were trading firmly in the red by Monday lunchtime despite a positive start, with shares in the oil and mining sectors providing a drag.London's FTSE 100 was down 0.9% at 6,489 by midday, dropping sharply after reaching a high of 6,576.74 early on.This week will be the first full trading week of the year following the festive holidays and is set to be extremely busy in terms of economic data and macro events.Inflation figures and purchasing managers' indices (PMIs) from the Eurozone, a Bank of England rate decision and the US jobs report are all due for release over the coming days."So anyone who thought they could just ease themselves back into things with a comfortable week will have a bit of a shock coming," said analyst James Hughes from Alpari UK.Concerns about Greece leaving the Eurozone were also weighing on investors' minds this week. Prime Minister Antonis Samaras said the policies of opposition party Syriza, which is leading polls, could drive Greece into default and out of the 19-nation European single currency.Resource stocks hit by lower commodity pricesCompanies in the oil and energy services sectors were bearing the brunt of weaker crude prices again on Monday with Weir, Tullow Oil, BP and Shell registering heavy losses.Brent crude was down 1.9% at $55.35 a barrel, extending declines after hitting a fresh five-and-a-half-year low on Friday on the back of record supplies from Iraq and Russia.BP was also weighed down by speculation that the recent collapse of oil and weakness in the value of the rouble will hit its fourth-quarter results, due to its exposure to Russia through its stake in Rosneft.Mining stocks were also down, including BHP Billiton, Anglo American, Glencore and Rio Tinto, as copper prices fell for a third day. Copper hit its lowest in over four years the previous session.Travel companies were continuing to benefit from the fall in oil prices with Carnival, IAG and EasyJet among the best performers on the FTSE 100.Department store chain Marks & Spencer was trading in the red after analysts at Societe Generale downgraded their recommendation for the stock from 'buy' to 'hold'.GlaxoSmithKline was lower after JPMorgan Cazenove lowered the stock to 'underweight', while pharmaceutical peer AstraZeneca was upgraded by the US bank to 'neutral'. Smaller counterpart Hikma Pharmaceuticals was boosted after Jefferies lifted its stance to 'buy'.Market MoverstechMARK 2,960.21 +0.05%FTSE 100 6,489.46 -0.89%FTSE 250 16,053.96 +0.01%FTSE 100 - RisersCarnival (CCL) 3,015.00p +2.90%TUI AG Reg Shs (Post- 16/12/14)(DI) (TUIJ) 1,083.00p +2.65%International Consolidated Airlines Group SA (CDI) (IAG) 499.60p +2.59%Ashtead Group (AHT) 1,190.00p +2.15%easyJet (EZJ) 1,711.00p +1.66%Imperial Tobacco Group (IMT) 2,841.00p +1.32%Land Securities Group (LAND) 1,166.00p +1.22%Travis Perkins (TPK) 1,859.00p +1.20%Reckitt Benckiser Group (RB.) 5,225.00p +1.16%British Land Co (BLND) 770.50p +1.12%FTSE 100 - FallersWeir Group (WEIR) 1,793.00p -4.78%Tullow Oil (TLW) 398.50p -3.77%Royal Dutch Shell 'B' (RDSB) 2,162.50p -3.27%BHP Billiton (BLT) 1,333.00p -3.27%BP (BP.) 397.20p -3.23%Glencore (GLEN) 287.65p -3.18%Anglo American (AAL) 1,149.50p -3.00%Marks & Spencer Group (MKS) 462.80p -3.00%Rio Tinto (RIO) 2,881.50p -2.98%BG Group (BG.) 839.80p -2.82%FTSE 250 - RisersHikma Pharmaceuticals (HIK) 2,111.00p +6.51%Bank of Georgia Holdings (BGEO) 2,187.00p +3.80%Ted Baker (TED) 2,263.00p +2.86%Poundland Group (PLND) 330.90p +2.83%Ocado Group (OCDO) 427.50p +2.79%RPC Group (RPC) 514.50p +2.29%Pace (PIC) 348.40p +2.29%Man Group (EMG) 164.30p +2.11%BTG (BTG) 820.50p +2.05%Rathbone Brothers (RAT) 2,037.00p +1.90%FTSE 250 - FallersWood Group (John) (WG.) 584.00p -5.12%Premier Oil (PMO) 157.00p -4.68%Drax Group (DRX) 435.10p -4.27%Hunting (HTG) 503.00p -4.01%Vedanta Resources (VED) 556.00p -3.89%Petrofac Ltd. (PFC) 684.00p -3.80%Afren (AFR) 43.96p -3.62%Oxford Instruments (OXIG) 1,234.00p -3.59%Lonmin (LMI) 169.20p -3.37%Evraz (EVR) 147.40p -3.03%