In 1982, he started a language course to become proficient at Mandarin and in 1985, was posted to the Embassy of the United Kingdom, Beijing as second secretary.

[6] On his return to full-time civil service work in 1998, he was appointed the Director of Motor Vehicles at the Department of Trade and Industry.

Dennis was posted to New Delhi in 2001 to be Director for Trade and Investment and in 2003 he was made Deputy Head of Mission in Beijing.

[6] For a short time in 2009 Dennis worked in the Local Staff Strategy Review but was very quickly given the job of the Head of the Zimbabwe Unit at the Africa Directorate at the FCO.

In his time as Ambassador in Luanda, Dennis oversaw the signing of a Memorandum of Understanding and led "successful ... efforts to deepen cooperation between Angola and the UK".