Complex sentence: Heseltine acted as a consultant to Haymarket during his periods out of government office (1974-9 and 1986--90) and resumed management of the company after Masters retirement in 1999.
Split into simpler sentences: Heseltine acted as a consultant to Haymarket during his periods out of government office (1974-9 and 1986--90). Heseltine resumed management of the company after Masters retirement in 1999.