The sleek ad, set to the music of British composer Edward Elgar, is a play on Britain's 'engineering might'.
"Sleek and fast unstoppable machine" the film begins, shot in the style of a slick car commercial, which then pans out to reveal a laser-guided bomb - one of the weapons reportedly used in airstrikes by the Saudi Arabia-led coalition in Yemen.
The Defence and Security Equipment International (DSEI) exhibition, which runs from Tuesday, is held every two years in London.
"For me, as a proud Brit, this is completely unacceptable," said Dominic West, a British actor who has appeared in U.S. thriller series "The Wire" and voices the short film.
"We are providing aid to Yemen, but also selling weapons which are being used in a country where children are being bombed and starved," West said in a statement.
War crimes
It comes as Human Rights Watch accuses the Saudi-led coalition of war crimes over a series of air strikes which killed 26 children in Yemen in June.
"The attacks, which struck four family homes and a grocery, in one case killing 14 members of the same family, caused indiscriminate loss of civilian life in violation of the laws of war. Such attacks carried out deliberately or recklessly are war crimes," the New York-based HRW said.
Saudi Arabia leads an Arab military coalition that intervened in Yemen in 2015 to support the government of President Abedrabbo Mansour Hadi after Iran-backed Huthi rebels forced him into exile.
Men uncover the body of a girl under the rubble of a house destroyed by a Saudi-led airstrike in Sanaa, Yemen, Thursday, July 2, 2015 Source: AP
HRW is urging the United Nations Human Rights Council, which is currently in session, to return the coalition to its yearly "list of shame" for violations against children in war.
Saudi investigation clears itself
Meanwhile a panel set up by the Saudi-led coalition fighting in Yemen to investigate civilian casualties found a series of deadly air strikes largely justified on Tuesday, citing the presence of armed militiamen at the homes, schools and clinics that were targeted.
The Joint Incidents Assessment Team said it had discovered mistakes in only three of 15 incidents it reviewed, and maintained the coalition had acted in accordance with international humanitarian law.
The coalition has been repeatedly criticised for civilian casualties. Human Rights Watch accused it on Tuesday of war crimes, saying air strikes that hit family homes and a grocery store were carried out either deliberately or recklessly, causing indiscriminate loss of civilian lives.
Young students sit in a former classroom at their local school in Saada City. Students now attend lessons in UNICEF tents. Source: Getty
"Until the moment of preparing this report, we have not found serious intentional violations in Yemen" said Mansour Ahmed al-Mansour, legal advisor for the Joint Assessment Team.
"The presence of innocent civilian victims in the war is because of mistaken bombardment and the presence of mistakes, this exists and we have previously said that."
UN blacklist
The UN blacklisted the coalition after concluding in a report released one year ago that it had been responsible for the majority of children's deaths in Yemen.
But in an embarrassing climbdown, the world body then announced that the coalition would be removed from the list.
The then UN chief Ban Ki-moon admitted at the time that the decision was influenced by threats from Saudi Arabia and its allies to cut off funding to UN aid programmes.
Saudi Arabia holds a seat on the 47-member Human Rights Council, re-elected in October last year in a vote sharply criticised by rights groups.
