Mr Blair's official spokesman said the letter would not be made public. But he said the gist of it was that "enough was enough".
President Bashir of Sudan was clearly not complying with the agreement that had been reached earlier this year, he said.
Therefore the Prime Minister believed that it was time for a new, tough UN resolution which would mean targeted sanctions aimed at the top members of the Sudanese Government and those supporting them.
Despite the signing of the Darfur Peace Agreement by the Government of Sudan and Minni Minawi's section of the Sudan Liberation Movement in 2006, conflict continues in Darfur, western Sudan.
It is largely a battle for resources, land, water and grazing rights together with a related struggle for power within the indigenous tribal administration structure.
Mr Blair will discuss his proposal with fellow EU leaders at a summit in Berlin this weekend. - 10 Downing Street
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