Speciality chemicals group Elementis was the strongest riser on the FTSE 250 saying it delivered a "resilient performance" for the three months ended September 30th and saw a return to more normal trading patterns in oilfield drilling.Premier Oil shares rose after the company this afternoon announced that first production from the Rochelle gas-condensate field in the UK North Sea has commenced. Serco shares climbed after it said its Chief Executive Chris Hyman had resigned as the firm unveiled a restructure of the business and plans to beef up its board in a bid to rebuild its damaged relationship with the UK government. SVG Capital was also on the up after reporting that it had seen a near 4% increase in its net asset value during the third quarter, helped by the positive share-price movements of two of its three-largest investments.Meanwhile, house-builders were broadly lower, with both Taylor Wimpey and Barratt Developments both sitting in the bottom 10. FTSE 250 - RisersElementis (ELM) 267.40p +9.46%Premier Oil (PMO) 347.30p +3.70%Grainger (GRI) 192.00p +3.56%Imagination Technologies Group (IMG) 290.80p +3.34%Fisher (James) & Sons (FSJ) 1,111.00p +2.68%Drax Group (DRX) 670.50p +2.13%Centamin (DI) (CEY) 51.30p +1.99%PayPoint (PAY) 1,049.00p +1.84%Computacenter (CCC) 559.50p +1.63%BH Macro Ltd. EUR Shares (BHME) € 20.15 +1.51%FTSE 250 - FallersTullett Prebon (TLPR) 309.30p -3.76%Millennium & Copthorne Hotels (MLC) 579.50p -3.34%Keller Group (KLR) 1,031.00p -3.10%Dialight (DIA) 1,154.00p -2.62%Taylor Wimpey (TW.) 110.70p -2.47%Synergy Health (SYR) 1,067.00p -2.47%Fenner (FENR) 409.00p -2.15%Barratt Developments (BDEV) 334.00p -2.02%De La Rue (DLAR) 850.50p -2.02%NMC Health (NMC) 353.80p -1.99%NR