Welshman Phillip Price, who led much of last week's British Masters before finishing in third place, held the same position Friday following his second straight 68. He was 8-under par, one shot ahead of Mark Roe (70), local professional Darren Prosser (68) and last week's winner Justin Rose (69).
Clarke, the winner of this event in 1999 and 2000, reeled off three straight birdies on the front nine at the Marriott Forest of Arden to grab the outright lead at 10-under. Steady rain rendered the course unplayable for a short time, however, and when Clarke returned he immediately bogeyed the 10th.
Although Clarke tallied a birdie at the 12th he dropped another shot at the next hole. When a birdie at 17 pushed him out in front once again, the 33- year-old from Northern Ireland wound up closing with a bogey to cap a back- nine, one-over-par 37.
'I played lovely for the first part but let a few get away at the end,' he said. 'But I am swinging the club very well and feel very comfortable. I am hitting a lot of good shots and a lot of good putts and just have to wait for a bit of luck.'
Clarke, who has finished top-10 on the European Tour Order of Merit each of the last six years, is seeking his ninth victory and his first since last year's European Open.
Drysdale, who earned a spot on tour this season by finishing fourth at last year's Qualifying School Finals, followed up his opening 68 with a 67 for the first back-to-back sub-70 rounds of his short career.
The 27-year-old Scot has birdied 13 holes through two rounds and picked up shots at all four par-5s for the second consecutive day on Friday. He hit 12 of 14 fairways and 13 of 18 greens in the second round, while showing his skill on the putting surfaces by taking just 26 putts.
'I'm playing the par-5s really well, which has been the key for me,' said Drysdale, who is leading a European Tour event for the first time. 'If I'm in the last group it will be a totally new experience for me, but I'm looking forward to it.'
France's Raphael Jacquelin, the runner-up here last year, headed into the weekend three shots off the pace after a 68. Also at 6-under 138 were Sweden's Dennis Edlund (70), Didier De Vooght (71) of Belgium and first-round co-leader Jarrod Moseley (73) of Australia.
Defending champion Peter O'Malley shot 69-76 to miss the 36-hole cut by two strokes. The cut fell at 1-under-par 143 and included 81 players.
Full-field scores from The Compass Group English Open