Promoted major on 30 September 1987, Cook was appointed a Member of the Order of the British Empire in April 1988 in recognition of further "distinguished service" in Northern Ireland. He transferred from the Staffordshire Regiment to the Devonshire and Dorset Regiment on 4 September 1990. Cook was promoted lieutenant colonel on 30 June 1994, and advanced to Officer of the Order of the British Empire in 1995 for his services in Northern Ireland between 1 October 1994 and 31 March 1995. He subsequently took part in NATO operations in Bosnia and Herzegovina in 1995 and was awarded a Queen's Commendation for Valuable Service. Promoted colonel on 30 June 1998 and brigadier on 31 December 1999 (with seniority from 30 June), Cook commanded the 20th Armoured Infantry Brigade from 1999 to 2001. He retired from the British Army on 1 June 2004.