Complex sentence: His career aggregate of runs was the highest in Test cricket until surpassed by Colin Cowdrey in 1970; his total of 22 Test centuries remained an English record until Alastair Cook surpassed it in December 2012.
Split into simpler sentences: His career aggregate of runs was the highest in Test cricket until surpassed by Colin Cowdrey in 1970. He was the first person to hit 22 centuries in Test cricket and this total of 22 Test centuries remained an English record until Alastair Cook surpassed it in December 2012.