Positive discrimination is the only thing likely to significantly accelerate the rate of progress towards a more diverse judiciary, a Supreme Court judge has suggested.

Lord Sumption, who is also a former member of the Judicial Appointments Commission, said positive discrimination to increase the number of women and ethnic minority judges is not ‘desirable’, but he called for an ‘honest public debate’ on the issue, saying ‘it should at least be on the menu’.

Giving the Bar Council’s law reform lecture, he warned that selection on merit alone would take ‘a long time’, maybe up to 50 years, before the bench reflected the makeup of the society it serves.

In April of this year, 23% of the judiciary of England and Wales were women, compared with 51% of the population at large; 4% were from ethnic minorities, compared with 12% of the population at large.

The proportion of both women and ethnic minority office-holders is at its highest among district judges, masters, registrars, costs judges and deputy holders of these offices. In these categories it varies between 26% and 33%. The numbers tail off as one moves up the judicial hierarchy - 16% of High Court judges are women and 4.5% are from ethnic minorities, Sumption said.

And the Supreme Court, with the exception of Lady Hale, consists entirely of white males.

While the problem begins with an educational system which ‘tends to perpetuate disadvantage’, Sumption said that the proportion of women in the judiciary has doubled since 1998, and the proportion of ethnic minority office-holders has trebled.

Sumption put this down to a stronger awareness of diversity as an issue among those responsible for selecting judges, and the natural consequence of the progressive increase in the proportion of female and ethnic minority practitioners entering the legal profession since the 1960s.

The problem, said Sumption, is not the direction of change, but the speed. ‘The ambition and talent required for a career leading to appointment as a judge is randomly distributed throughout the population. It is not the preserve of any one gender or ethnic group. It follows that selection on merit alone can be expected eventually to produce a diverse judiciary.’

But he said: ‘It will happen only over a considerable period of time. In the short term, accelerated progress towards a diverse judiciary is not going to be achieved under a system of appointment on merit alone.

‘Without some kind of positive discrimination, the judiciary is never going to be significantly more diverse than the pool from which it is drawn, and the pool from which it is drawn is not the population at large, but the legal profession,’ he said.

‘We need, as a society, to have an honest public debate about the hitherto unmentionable subject of positive discrimination.’

While there are arguments on both sides, he said: ‘The real problem is that the debate has not happened… because of the conventional assumption that merit and diversity are compatible, even in the short term.’

‘Selection on merit is only compatible with a move to a diverse bench over a considerable period of time, we have never thought seriously enough about the choice to be made between them. I doubt whether we can afford to tiptoe round these issues for much longer.’

But he also warned of a ‘patronising’ effect. ‘Those women and ethnic minority candidates who have been appointed under the current system are justifiably proud of having achieved this under a system based exclusively on individual merit.

‘A partial abandonment of that principle would therefore be likely to make judicial office a great deal less attractive to the very people that its proponents are trying to help.’