"He is confident he can hand over the Bill to the Commons with its central planks intact, and not too diluted," said a senior aide. "However," she conceded, "there will obviously be a battle in the Commons."
It is remarkable that such a seemingly uncontentious piece of legislation, the product of a consultative Green Paper, then a government White Paper and finally a Cabinet-approved Bill, could have aroused such passionate hostility - chiefly, though not exclusively, on the Tory Right.
Much of the blame - or praise, depending on your point of view - for the excoriation that has been heaped on the 68-year-old devoutly-Christian Lord Chancellor may be laid at the door of the Daily Mail, whose propaganda guns have been booming away since last October. In tabloid terms, Lord Mackay of Clashfern stands convicted as "a subverter of family values".
Yet, say friends, the life peer appointed nine years ago by Lady Thatcher is privately committed to the reform, which originally stemmed from the Law Commission. "He often says: 'you cannot force people to love each other or stay together. You have to deal with the realities'," said one.
The Family Law Bill will allow divorce after a year without apportioning blame to either partner. Its critics in the Lords, led by the formidable Baroness Young, former Tory leader in the Upper House, believe it is wrong to ditch the concept of fault, and that a year is not long enough to wait for the dissolution of a marriage.
She argues: "Every piece of divorce legislation has increased the number of divorces. I think that is what is going to happen again. That is the message this legislation is going to convey. Far from being a Family Law Bill, it is a Divorce Bill. It is designed to make people who are divorcing feel better about it."
But Lord Mackay's aides, while admitting that he is "frustrated at the slow progress" of the Bill, do not believe he will sacrifice its central pillars. "I would be extremely surprised if he makes further amendments," said one. "He is certainly not minded to do that. And he is much wilier than these people realise."
One aspect of the Bill will almost certainly have to go, however. The controversial issue of splitting pensions is so complex that it will be hived off to the other Lord Mackay - of Ardbrecknish - at the Department of Social Security.
If, as expected, the Bill clears its hurdles in the Lords, it still faces stiff opposition in the Commons. Sir Rhodes Boyson, a member of the executive of the Tory 1922 back-bench committee, echoes the concern of Conservative MPs. "I am not happy about it," he admits. "There is concern in the party, and not just those of us with religious views, that we have made divorce too easy. For a long time, there has been a movement towards easier divorce, but the tide is now running the other way. There is a feeling that in the interests of children, it should be made more difficult."
Julian Brazier, Tory MP for Canterbury, president of the Conservative Family Campaign, which has the support of 25 MPs, will seek to restore the concept of fault.
However, with a free vote of MPs, the Government will be able to count on the support of most Labour members. It will be "a major struggle" to halt the reform in the Commons, Mr Brazier admits.
Instead of outright rejection of the Bill's central provisions, Tory back-benchers will seek greater emphasis on reconciliation, and a tightening- up of court procedures for awarding the custody of children and the division of assets. Particular scrutiny should be made of a divorced wife's new partner, he argues, because they are the largest single category of child sex abuser.Reuse content