'Why remain in a country that sent our son to an unjust war?'

Ann Lawrence and her husband George are planning to emigrate. Almost exactly a year ago, they lost their only son during the Iraq war. They believe they have now given Britain enough.

Marc Lawrence died on 22 March - two days after the invasion began - one of six Royal Navy officers and an American killed when their two Sea King helicopters crashed head-on, in bitterly contested circumstances.

Since then the Lawrences' grief has hardened into anger, and their dreams of eventually retiring to southern France have become concrete plans. They are now convinced that Marc's life was wasted on an "unjust" war - and have accused Tony Blair of doing so in writing.

In a forceful letter to the Prime Minister, written 16 days after they buried their 26-year-old son, a lieutenant, in June last year, the Lawrences blamed Mr Blair directly for his death. Their letter stung Mr Blair into a two-page response in which he sought to justify the war.

The Lawrences wrote: "Our son had a bright future. The choice you made has eliminated this future and that of other victims of your war. [The] overthrow of the Iraqi regime was a good thing, but the means by which you brought this about were at best questionable and at worst dishonest."

Writing on Sunday 20 July, Mr Blair was under the greatest stress of his political career. It was three days after the suicide of Dr David Kelly, the biological weapons expert who was outed by the Government as the source of a BBC story on the Government's Iraqi arms dossier.

And his hand-written letter, released by the family to The Independent on Sunday, offers an unusually intimate insight into the Prime Minister's thinking.

He admitted immediately "there is little I can say to mitigate your grief or anguish", and, referring to the furore surrounding Dr Kelly's death, said the "current public debate must make things worse".

But he insisted the coalition would find definitive proof that Iraq possessed chemical and biological weapons. "Your son made a sacrifice which, in time, will be recognised as being made to defeat the criminal threat to our security in the modern world," he wrote.

The Lawrences profoundly disagree. Their trauma has been worsened by the collapse of the Government's case for war, by the 73 days it took before they found his body on the seabed, and, more recently, by serious doubts about the true cause of Marc's death.

Earlier this year, The Independent on Sunday revealed that an official board of inquiry into the crash had found potentially fatal shortcomings in the equipment fitted to the Sea Kings and the operational rules in force that night. But, to the couple's disquiet, senior Navy officers and the armed forces minister, Adam Ingram, have suggested the crew were to blame. Under official flying rules, pilots are responsible for their own safety.

The Lawrences' anguish will be intensified tomorrow - the first anniversary of the Sea King crash. The couple will be in Portsmouth for a private memorial service to the seven officers who died.

Mr Blair's distress at their grief has not impressed them. "Would it have been any different if he had been run over on his motorbike?" said Mrs Lawrence. "It was an accident that shouldn't have happened and a war that was unjust."

The Lawrences are convinced the war is about Iraqi and Middle Eastern oil reserves, not democracy. "There are other regimes which are just as terrible in this world, but we're not so worried about them. Presumably because they've not got oil," said Mrs Lawrence. Mr Lawrence, speaking at the couple's home in the small Kent town of Westgate on Sea, added: "Blair and Bush are two mischievous boys taking sticks and disturbing an ants' nest, and the ants are going to fight back."

Ultimately, however, the couple have decided to emigrate. "We want to get out. We'd already planned to buy a house in France. Marc wanted us to do that," said Mrs Lawrence. "I can't stay here. They've had too much from us. I don't want to give anything else to this country. I'm a nurse, my husband a fireman and my daughter a teacher, but I want to contribute nothing else. This country is corrupt and it starts at the top."