The biggest expansion of the EU in its history to 25 members is "good for Europe and good for Britain", UK Prime Minister Tony Blair has insisted.
Blair: New members will be a catalyst for European change
The 10 accession countries were also "keenly aware" of the role the US had played in helping them achieve their freedom, Mr Blair writes in The Times.
The new states, which join the EU on Saturday, share the same views for Europe's future policies, he said.
The move to push for enlargement "will be seen as the right one", he added.
'Catalyst for change'
Mr Blair's article appears just days after his U-turn decision to hold a referendum on the EU constitution.
Conservative leader Michael Howard outlined his party's opposition to an EU constitution on Thursday, by claiming: "We don't want to be part of a country called Europe."
The nations joining the EU are: Cyprus, Czech Republic,
Estonia, Hungary, Latvia, Lithuania, Malta, Poland,
Slovakia and Slovenia.
Writing in The Times, Mr Blair says: "I believe ...that the accession tomorrow will be a catalyst for change within the EU, helping to give a new push to Britain's agenda and fresh impetus to priorities which are already in the ascendancy in Europe."
He reiterated his warning that "no one will be able to come from the new accession countries to Britain simply to claim benefits" or be eligible for housing "unless they are economically active".
But Mr Blair stressed: "I am equally determined that we continue to welcome those whose skills, talents and energy we need.
"To fail to do so would be damaging for our economy and against our national interest."
Mr Blair said it would be no surprise that countries that have regained their freedom from the "dead hand of communism", would want to preserve this independence within the EU.
"They share the British view that their future prosperity rests on a liberal, competitive economy," he said.
The prime minister pressed his belief that the best way to combat the threat of global terrorism and to protecting our freedoms was by "preserving and strengthening the transatlantic alliance".
He said English was the second language in most of the new EU countries and they appreciated the role the US had played in helping them to achieve their freedom.
"Europe is strongest and most effective as America's partner, not its rival or servant."
Mr Blair said he was convinced the decision to push for enlargement was the right one.
"I believe that the new members will help us ensure Europe is ready to meet the difficult challenges of the future."
He added: "Tomorrow's expansion of the EU to the East and South is good for Europe and good for Britain. Good for our security, for our jobs and prosperity.
"This weekend we should send a clear message to the 10 new EU members: Britain will be your allies and partners in making the new Europe work, just as we were proud to be on your side as you worked towards EU membership."