Mr Whitson succeeds Brian Goldthorpe, who will take charge of risk management in Hongkong Bank's parent, HSBC Holdings.
Midland confirmed that Gene Lockhart, chief executive of UK banking, is to leave, as his job has disappeared following the HSBC takeover. Mr Lockhart has a contract with three years' notice and a salary of pounds 400,000, so could claim pounds 1.2m. His share options would give a pounds 500,000 profit.
George Loudon, chief executive of Midland Montagu, is thought to be Midland's second-highest- paid executive on pounds 395,000 a year, and could claim almost pounds 1.2m, plus another pounds 200,000 profit on options.
HSBC Holdings, the new parent of Midland, has given no indication of whether it will agree to the full payout of pounds 3.1m.