Premier Oil is leading the FTSE 250 risers after a successful drilling result at its 35% owned Catcher East 28/9 licence in the UK Central North Sea. The estimated find of 300m recoverable barrels is the biggest in the North Sea for years and could be worth over £7bn. Partners Encore and Nautical also rocketed on the back of the news. Shares in Connaught slumped again after the social housing firm last week lowered its estimates for this year and next year because of the emergency budget.Online gaming company PartyGaming is slightly lower despite having been awarded licences by the French gaming regulator, ARJEL, to run online poker and sports betting web sites for French residents. The group can offer sports betting immediately but will have to wait a short while before the French poker market is opened. The regulator is expected to give clearance for poker offerings later this month.Senior, the manufacturer of high technology components and systems, is trading in line with expectations with profits for the first half of 2010 expected to be well ahead of last year. The shares are also down.FTSE 250 - RisersPremier Oil (PMO) 1,267.00p +7.19%Lamprell (LAM) 225.10p +4.50%Computacenter (CCC) 293.70p +3.74%Meggitt (MGGT) 320.00p +3.23%Bodycote (BOY) 205.30p +3.22%Kesa Electricals (KESA) 120.20p +3.18%Filtrona PLC (FLTR) 219.80p +2.90%Spirent Communications (SPT) 110.50p +2.70%Gartmore Group (GRT) 114.20p +2.61%Mondi (MNDI) 402.50p +2.55%FTSE 250 - FallersConnaught (CNT) 149.90p -30.28%Go-Ahead Group (GOG) 1,091.00p -6.51%Senior (SNR) 126.00p -3.60%PartyGaming (PRTY) 244.30p -2.67%Berkeley Group Holdings (BKG) 780.50p -2.56%Micro Focus International Plc (MCRO) 425.30p -2.52%Kier Group (KIE) 963.00p -2.48%Logica (LOG) 109.10p -2.33%Beazley Group (BEZ) 116.60p -2.26%Galiform (GFRM) 62.35p -2.04%