The number of UK armed forces personnel lost since the start of the war on Iraq stands at 20.
British troops have been in heavy fighting
Just two of them have been infantry soldiers killed by Iraqi fire.
The latest deaths were two soldiers from the Queen's Royal Lancers, part of the First Royal Regiment of Fusiliers Battle Group, killed by 'friendly fire' on the outskirts of Basra on Tuesday.
Monday saw the death of a soldier from the 1st Battalion Black Watch, killed in combat at al-Zubayr, near Basra.
The first British combat victim was Sergeant Steve Roberts, from Bradford, who was believed to have been shot during rioting also at al-Zubayr on Sunday night.
The 33-year-old died from his injuries on Monday morning.
The first British 'friendly fire' deaths of the war came on Sunday when an RAF Tornado was downed by a US Patriot missile as it returned from a mission over Iraq.
Flight Lieutenant Kevin Main, a pilot, and Flight Lieutenant Dave Williams, a navigator, both of 9 Squadron, were lost in the incident.
Saturday morning saw the catastrophic collision of two Sea King helicopters from the Ark Royal.
Lieutenants James Williams, 28, Philip West, 32, and Antony King, 35, were among six Royal Navy officers from RNAS Culdrose in Cornwall who were killed.
The first accidental loss of life in the conflict also came from a helicopter crash, over the Kuwaiti desert after just 24 hours of the war.
Eight Royal Marines from 3 Commando Brigade in Plymouth lost their lives in the Sea Knight, as well as four US servicemen.
Six of them have been named as Captain Philip Guy, 29, Colour Sergeant John Cecil, Ian Seymour, Mark Stratford, Sholto Hedenskog and Llywelyn Evan.
Captain Guy's wife Helen, due to give birth in two weeks and already with a
20-month-old son Henry, said her husband was "the most brave, courageous man you could ever imagine".
"I know he died a true hero. He died for his Queen and country and to make the world a safer, better place for us to live in, for his children to grow up in," she said.
The family and friends of Sergeant Cecil also paid tribute to him.
A statement from his family said: "John leaves behind a great many friends and relatives, and our thoughts go out to Wendy Cecil, his children Nicholas and Jodie, his beloved daughter Paige, and his brother David Cecil, who all reside
in the Plymouth area.
"John was proud to be a Royal Marine, proud to be British and proud to represent his country, a country dedicated to making the world a safer place to live in."