RLAM Corporate Governance Manager Ashley Hamilton Claxton said the move was "a clear violation of an important corporate governance principle designed to protect shareholders and ensure effective independent oversight of the company's management".

The asset manager also opposed plans to keep paying Heavey his CEO pay and perks package for the first six months of his role as a non-executive chairman.

RLAM also opposed Tullow's remuneration report, remuneration policy and the election of the Chairman of the Remuneration Committee at Tullow, given ongoing concerns that pay is too focussed on the short term, it said in a statement.

RLAM said it holds 8.66 million shares in Tullow Oil, 0.95 percent of the company.

(Reporting by Simon Jessop; editing by Carolyn Cohn)