"It's not for me to point out that sort of thing. These are elected members of Parliament; they are put there by their constituents to represent their interests and they have to do their best to do that."
He is smiling now, but last autumn Lord Mackay was in the deepest crisis of his tenure as the longest continuously serving Lord Chancellor of the century. For a week it seemed to be touch and go, when at the end of the session of Parliament a Daily Mail-inspired campaign by a handful of Tory backbenchers frightened the Government into dropping the Family Homes and Domestic Violence Bill.
Suddenly the Divorce Bill's place in the Queen's speech seemed to hang in the balance. He was caricatured as a well-intentioned but naive man who had been hijacked by the liberals and the politically correct into pushing through a charter for live-in lovers. There was even talk in Westminster of him resigning. Then almost as suddenly the crisis was over, the Government pressed ahead, and both Bills were back on track.
Sitting in his office in the palace of Westminster the morning after completing the committee stage in the Lords of what is now the Family Law Bill, combining both earlier measures, Lord Mackay says of the backbenchers who hijacked the Family Homes and Domestic Violence Bill: "It could happen to any legislation - it's a question of whether you feel you could contribute or become knowledgeable and I'd be surprised if there are not other areas of legislation where at least some MPs are not fully familiar with every detail of the Bills."
In short, people opposed the Divorce Bill because they did not understand the reality of the present system, he believes.
He is not taking the parliamentary process for granted, but is hopeful that it will now go ahead with slight compromises on the length of time for divorces where the settlement has not been agreed - likely to increase to 12 months from six - and possibly by splitting pension funds on divorce rather than on retirement.
Last autumn's crisis was complicated by the concurrent row between Michael Howard, the Home Secretary, and the judges over his plans to introduce minimum sentencing. Lord Taylor, the Lord Chief Justice, on behalf of the judges, criticised the plan with an unprecedented public statement saying it was misguided to reduce judges' discretion. Long sentences did not deter crime. Lord Mackay, as a member of the Cabinet but head of the judiciary, found himself straddling a constitutional precipice. The Bar Council chairman, Peter Goldsmith, called on him to leap publicly on to the side of the judiciary. Mr Howard and the Tory party chairman, Brian Mawhinney, wanted him to leap their way.
But speaking publicly about his dilemma for the first time, Lord Mackay made it clear he has found a judicially chosen position in the middle which he can live with. There is no constitutional crisis, he believes.
"Parliament usually fixes a maximum penalty, and in principle it doesn't seem to me there's much difference between a maximum sentence and a minimum. The two are restrictions on a judge's unlimited discretion. That is nothing whatever to do with a judge's independence. The judge is independent of the executive in deciding the sentence within the limits Parliament has laid down, and it's for Parliament to consider ultimately what the right rule should be. I've no doubt Michael Howard intends to bring proposals before Parliament as soon as he has the opportunity. Parliament will have to decide, and the judges will have to apply the law, will willingly apply the law as laid down by Parliament."
The role of the Lord Chancellor as head of the judiciary and spokesman for its views in Cabinet is to be consulted but not to have a veto on legislation. Has Lord Mackay been playing peacemaker? "I have an ongoing discussion with judges on a whole lot of matters and also with Michael Howard and a whole lot of colleagues on these matters and I think that's as far as it would be appropriate for me to go."
But at the same time it appears he has been able to extract a small concession in return for this almost unequivocal public support. "There is a question of whether the minimum should be absolute ... or whether there should be permitted exceptional cases in which the judge would not be obliged to apply the minimum." He understands that Mr Howard is still considering and consulting on his definition of "exceptional". The Home Secretary had talks with penal experts including judges over the weekend.
Although the longest serving Cabinet minister in the Government, he has never been a politician, although in his decade and more in office he has learnt political skills. His method is to take a long time to decide in his mind what what he thinks is right, then hope to persuade everybody else. If he is right, most people will eventually recognise that, and opponents will fade away.
That process is about to enter its second stage with legal aid, which appears to be the battle his mind is focusing on next, with family law probably safe, or at least safely left to others. He has been given an adroit new junior minister, Jonathan Evans, to help to steer it through the Commons.
The protracted consultation period on the legal aid Green Paper is now over. It proposes to make legal aid available only through franchised solicitors' firms holding contracts for each geographical district and area of law. Lord Mackay remains convinced that it must be better to give legal aid for the most worthy cases, rather than only to the very poor, as now. He says he hopes to produce a White Paper around Easter or not long after.
But go ahead he will, although he says he will not rush in with proposals not sufficiently worked out. "The question is how proposals are developed. Things can be made to work by proper adjustment of the detail." The process will be one of gradual refinement.
Perhaps most controversially, he has still not apparently ruled out some form of capping of both civil and criminal legal aid budgets. He says: "I'm looking for a system under which legal services provided by the state could be delivered for a given sum of money, and priorities assigned within that on a national and possibly local level."
Many solicitors, fearing they will lose income, oppose the changes. Barristers have an even more fundamental objection, asserting that the legal aid reforms proposed in a Green Paper last year are unworkable because they would require a means of judging the quality of advocacy, something which they say cannot be done.
Everyone accepts that a barrister's success rate alone is clearly too crude. The logic of fundholding solicitors is that the less they spend on each case, the more profit they make on the contract. So how, the Bar asks, do you make sure they use a good enough barrister where necessary?
Lord Mackay sees it as his duty to get the best value for money for the taxpayer. "It's no good saying you can't measure quality," he says in reply to the Bar's objections. "We have to try to devise methods. That's one of the things that makes me hesitant about saying when we must go forward - we have to work at this quite hard. There are all sorts of problems." Problems to which, with the clock ticking, he apparently still has no answers.