On the other hand the proportion of London state-school children receiving free meals almost doubled between 1991 and 1996.
Research recently carried out at the University of Greenwich shows that employers make the greatest cash contribution to post-school education and training. But part-time, temporary or black workers are less likely to receive employer support for their training than full-time, permanent or white employees.
So the brunt of responsibility for continuing education of less well-off Londoners falls to the further education colleges.
If we want to enable people to escape from social exclusion, we need to know how they fare during their "second chance" in FE. The pass rates on the qualifications they take could be the most useful way of measuring this.
The Further Education Funding Council publishes pass rates in its annual performance indicators for colleges, but something very odd has happened to these statistics. Out of the 439 colleges in England, 47 had no rate calculated at all, while a further 22 had rates recorded as in need of adjustment. London is one region most affected by this lack of accuracy.
Why is it so difficult for colleges to find out how students have fared with their exams or assessments? The main reason must surely be the chaotic state of qualifications in this country. Colleges in London have to deal with 229 examining bodies.
Seventy-five per cent of London students were taking courses that have not been absorbed into the national framework of qualifications, although many of these are valued by employers.
So far, public debate about qualification reform has concentrated on reducing unnecessary divisions between GNVQs and A-levels, or on bringing City amp; Guilds and BTecs into the framework. These changes, however valuable would leave most of the college curriculum untouched. Rationalisation needs to centre on major course groups like adult basic education, computer literacy and word processing, and (especially important in London) English for speakers of other languages.
With London pass rates apparently much lower than in other English regions, the research used anonymous records of individual students to look behind the figures. The level and subject of study make a difference to success, as do the students' age and gender.
But the most striking fact was that while half the white students passed their main qualification aim, less than a third of black African or black Caribbean students passed. Pass rates were low for all the other ethnic minority groups as well, and these general patterns are unlikely to be affected by the inaccuracies in the data.
Differences in achievement are unlikely to be confined to London, but it is there that the greatest numbers will be affected because ethnic minority students tend to be concentrated in the capital.
These differences in pass rates point towards worrying levels of institutional racism. But they do not tell us where the main obstacles to black people's aspirations are to be found. Possibly, it is social and financial circumstances that make successful study much more elusive for some people than others.
There may also be attitudes, however unconscious, in the colleges that damage the prospects of a large contingent of their students. And some blame could well be placed with the previous continual erosion of government funding for FE, which has particularly affected London.
The FEFC should start publishing national pass rates for students of different ages, sexes and racial groups.
Yardsticks of achievement are vitally important, so all qualifications need to be brought into a common framework. Only then will we be able to see how institutional discrimination is to be rooted out.
Judith Watson is a senior research fellow at the University of Greenwich