Bell,whose international average is now down to 15, lasted three balls before being dismissed by Mills. He was not the only one to be out for a duck as Paul Collingwood followed shortly after.
That left England on 83-5 but Kevin Pietersen and Warwickshire's Tim Ambrose saved the innings. Pietersen went on to complete his century whilst Ambrose, who won't keep wicket due to a back injury, passed the fifty mark with ease.
Pietersen was finally out for 115 whilst Ambrose batted until just before the close of play when he was caught by Hopkins off the bowling of O'Brien for 67. England closed on 273-7
Warwickshire travel to Glamorgan tomorrow for a County Championship game at Cardiff. Ashley Giles side are second in the Division Two table with the Welshmen seventh.