Many people were shocked when they learnt that I had decided to send my son James, 12, to a private school. But, in some ways, nobody was more surprised than me. I admit that anything I say is hypocritical and that I am defending the indefensible, but I wanted to explain why I took the decision I did.

If you had told me 10 years ago that I would do such a thing I would not have believed you. For many socialists, public versus private education is a defining issue of principle. Labour supporters, who otherwise have all the trappings of an upper-middle-class lifestyle, go to elaborate lengths to send their children to state schools.

It has become a conscience issue. When Harriet Harman chose to send her son to an opted-out grammar school a few years ago I was supposed to have said that she “made the Labour party look as if we do one thing and say another”. All I can say is that I don’t remember saying that, and nor does Harriet. She is a good, supportive friend and was one of the first to call me when this story broke. It is true that my local party in Hackney would definitely prefer that I had sent my son to a state school but no one has been unpleasant.

The question of private education was not always such a problem for those in the Labour party. No one remarked when Harold Wilson sent his children to private school. It did his reputation as a man of the left no damage.

Schools only became a conscience issue in the 1970s. Perhaps the reason the issue is so emotive is because in England education is wrapped up with notions about class. Choosing a private school is synonymous with propagating the class system. However, like many immigrants, I see education as the most important gift I can give my son. My parents left school at 14 but were determined to give me the best education they could; I feel the same way. And there are many black and Asian children at the private school I have chosen who are of the same view.

That said, I have always shared my party’s deepest prejudices about private education. I was educated in the state sector and I went on to Cambridge University. I was surrounded there by people who had been privately educated. Nothing that I saw at that time led me to believe I had missed out. On the contrary, I still believe that a good state school education is as good — or better — than anything the private sector can offer. So I well understood the vitriolic response to my decision.

So why have I done it? I worked out some time ago it is not possible to be a good mother and a good MP. There were school assemblies I missed, the concerts I did not get to and the many years when my son only saw me in the mad scramble to get him to school — I came home from Westminster long after he had gone to bed. But just this once I decided to put him first. I would have done anything not to have found myself in the position I was in this year. I had to choose between my reputation and my son. I chose my son.

The reason I had to make this choice is because of the catastrophic failure of black boys in Britain’s schools. I have campaigned around black underachievement in schools for the best part of a decade; setting up a study group called Black Men in Crisis in 1995; holding a series of conferences on this issue and recently launching the London Schools and the Black Child initiative.

Nationally, 42% of boys get five good GCSEs. But in Hackney only 9% of black boys achieve this. This is a frightening statistic. Worse still, while other ethnic groups are catching up with white children or even overtaking them, black boys continue to fall further behind. Their underachievement is linked to a youth culture that can lead to the fringes of criminality. And even gun crime.

I had my son at 37. Most of my friends and relatives had their children in their late teens and early twenties. So I watched their struggles with their sons and school. Some of these women were white-collar professionals, others were ordinary grassroots women. They all faced the same challenges with a system that has been failing black boys for three generations.

Their advice to me was emphatic and always the same. Do not sacrifice your son to your principles. Choose the best school for your son, regardless.

There were also specific problems in relation to Hackney, which is one of the London education authorities that has struggled ever since the abolition of the Inner London Education Authority. The government has tried privatisation to raise standards. That did not work. And now they have taken education away from the local authority and given it to the independent Hackney Learning Trust.

Probably, Hackney was always too small, too underfunded and too loaded with multiple social deprivation to provide proper education without more external support. The government has moved in the right direction by appointing a London commissioner for schools. But there is a long way to go.