A sunset repatriation ceremony was previously held at the military's contingency operating base in Basra yesterday evening before the coffins were flown out of the southern Iraqi city.
After today's sombre service, the bodies were taken to John Radcliffe Hospital in Oxford where post-mortems will take place.
One of the soldiers killed in last Thursday's bombing was a close friend of Prince William.
Clarence House said at the weekend that that the prince had been "deeply saddened" to hear of the death of Second Lieutenant Joanna Yorke Dyer, 24, with whom he trained at the Sandhurst military academy.
Corporal Kris O'Neill, Private Eleanor Dlugosz and Kingsman Adam James Smith were also killed in the April 5th blast, when the Warrior armoured vehicle that the four soldiers was travelling in was attacked near Basra as they returned from a patrol.
The explosion, which left a 3ft deep crater in the road, also claimed the life of a Kuwaiti interpreter and seriously injured a fifth soldier.
A total of 140 UK service personnel have now been killed in Iraq since hostilities began, with 109 of those having died in action.
The latest military fatalities in Iraq come amid ongoing concern about the UK's involvement in operations there.
Yesterday a report published by the aid agency Oxfam warned that the government's "misadventure" in Iraq had compromised Britain's ability to intervene to protect human rights in other parts of the world.
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