To the new Labour government, as to the Conservatives, the battle to keep control over Britain borders has been one of the most crucial in the European debate.
Mr Blair can rightly argue that he has succeeded where his predecessors failed in securing legally binding guarantees that Britain's will not have to surrender its frontier checks, as part of the implementation of "border free Europe."
The deal will be presented to today as one sign that Labour's new "co- operative" approach to EU negotiation is paying off. However, weighed against his own original negotiating priorities, Mr Blair has had to pay a price for his success, and it is a price which could be a heavy one for his government to pay in the not so distant future.
Like the Conservatives, Labour originally demanded far more in the immigration debate than the right to maintain national frontier controls.
Britain was determined to stop other member states going ahead with their own plans to pool powers in areas of immigration and asylum. The main reason for the opposition was the knowledge that, as so often in the past, Britain was likely to be dragged in to the same common policies in the future.
In particular, the Government wanted to stop the new integration taking place within the so-called "first pillar", which is the hard-core of EU decision-making, and allows the European Commission, parliament and Court of Justice widespread powers.
Though Britain would have its "opt out" in these areas, the Government was strongly opposed to such a new swathe of integration and threatened to veto the move.
If other countries were determined to push ahead by pooling sovereignty in these areas Britain would have preferred it to happen only as a loose inter governmental arrangement.
However, creating an area of "freedom justice and security" was a main priority for other member states. Along with lifting internal borders the other Europeans want to put in place a common ring fence around the EU's external borders and harmonise their common internal security.
The other countries have won agreement to do this, and Britain has made no threat to veto, knowing this would be out of tune with its new Euro- friendly policy.
As a result, the new Amsterdam Treaty, to be finalised today, will lead to the far-reaching transfer to the European Union's first pillar institutions of vast powers over policies on immigration, visas, rights of third country nationals, asylum policy and reception of refugees.
Judicial co-operation on civil matters is also to become integrated. Meanwhile police cooperation is to be boosted under cooperation procedures, but may well move to the first pillar later.
Furthermore, after a transfer period of five years, decisions taken on many of the questions involved will be qualified majority vote.
Of all the elements of the new treaty the transfer of power to Brussels in these areas is by far the most significant. The new integration is not just a matter of institutional readjustment, or setting priorities for the future, it involves practical steps to formulate policy on some of the most sensitive issues.
The Government knows that if the EU's new common policies on immigration and asylum, combined with their attempts to secure greater police and justice cooperation, prove successful, Britain will probably inevitably be drawn in.
The deal over borders
What Europe will today grant to Britain on borders.
Britain is to receive a "legally binding" guarantee that it can maintain its frontier checks. There can be no threat, now or in the future, to Britain's sovereign control over its border. The guarantee will be firm enough to rule out any chance of any country challenging Britain's rights over borders in the European Court of Justice.
In addition, Britain maintains the right to make its own immigration and asylum policy and to enforce its own police and customs checks.
The Government has also won the right to "opt in" to European policies on immigration, asylum and police co-operation, should it wish to do so.
The agreement is therefore not officially described by a government spokesman as an "opt-out" but a right to "opt in."
What new power-sharing Europe's partners have agreed among themselves.
Other member states, except Ireland (which is with Britain on this) and Denmark (which also wants to keep sovereignty in this area) other member states intend to give up their sole sovereignity over immigration and asylum and allow Europe's institutions oversee a single policy.
Within a period of five years, the other member states intend to end all frontier checks between member states to create what they are calling an "area of freedom justice and security". This process has already been started by some member states under the so-called Schengen agreement.
At the same time, the countries will agree common rules on which third- country nationals should be accepted into their states as immigrants or refu-gees. They will agree on standards for treating immigrants and asylum- seekers and on "burden- sharing", whereby each state accepts it must take a fair number. The European Commission will take on new powers to issue proposals and laws in this area, and the European Court of Justice will oversee implementation.
After five years, the joint decisions will be taken by qualified majority vote, under the terms of the draft treaty text, to be finalised today.