Howell fired his lowest round of the year, a 7-under-par 65, to move to 11-under for the tournament. Karlsson held sole possession of the lead after a first-round 66. He then maintained a share of that lead by shooting a second-round 67.
Howell gained his first European Tour victory two years ago in the Dubai Desert Classic. He still in search of win No. 2.
Ive had a few chances but not loads to win, the 25-year-old said. But I guess my technique hasnt been good enough to contend week in and week out.
Karlsson won earlier this season in the Spanish Open. The 65 Swede has a habit of winning in odd years, having won in 1995, 97, 99 and now 2001.
I actually played better today than yesterday, Karlsson said. I hit a lot more fairways. It was a good day.
Mark McNulty is three shots off the pace. The Zimbabwean won this event in 1987 when it was contested on the Dukes Course.
This year, the event is being played on the new Marquess Course.
I just rode my luck today, said McNulty. I had a few lucky breaks. This is a happy hunting ground. Different course, but a happy hunting ground.
Colin Montgomerie (71), who started the day two off the lead, and Lee Westwood (70) are each six off the pace.
A total of 74 players made the halfway cut, which fell at even-par 144.
Full-field scores from the Victor Chandler British Masters