Oil giant BP said William Castell stepped down as the head of its safety committee in December and plans to leave the board in April as the reshaping at the top of the company continues in the wake of the Gulf of Mexico oil spill.

BP said on Friday that Castell, chair of its safety, ethics and environment assurance committee since 2008, would not seek re-election at the company's annual meeting in April.

Andrew Shilston will succeed Castell in the role of senior independent director, the company added, while Ann Dowling, head of the department of Engineering at the University of Cambridge, will join the board and safety committee.

The changes follow significant adjustments to the company's board over the last two years, many of which came after BP's Macondo well gushed 4 million barrels of oil into the Gulf of Mexico after an explosion in April 2010.

Castell was head of the committee at the time of the spill, when BP's safety standards were vigorously questioned. He passed leadership of the committee to fellow board member Paul Anderson in December 2011, BP announced on Friday.

Investors expressed their displeasure at Castell last year when 25 percent of investors who voted ahead of BP's annual meeting, representing 60 percent of shares, voted against his re-election.

Shares in BP traded up 0.5 percent at 480.6 pence.

(Reporting by Sarah Young and Tom Bergin; Editing by Rosalba O'Brien and Will Waterman)