Foster care has too long sidelined in British society and even more so since the New Labour government made adoption targets the primary focus of reform in this area of social care. Yet foster care, far more so than adoption, is truly about the needs of children rather than the unmet desires of substitute parents. This is not to demean adopters and their motives. But it seems to me indisputable that, with many exceptions, most adoptive parents are seeking a family for themselves (which is understandable and admirable) while almost all foster parents take up fostering to meet the altruistic impulse within themselves or to use their parenting skills to benefit a wide group of children.

Their role is almost superhuman. To care for children yet never lay claim to them or cross over into love, to pick up again from the last departed child and welcome in a new one perhaps for a night, perhaps a year, to meet professional requirements without ever getting the recognition that they are doing an indispensable job, to deal with the fallout of family and social failures and yet to remain invisible and taken for grantedÉ I am sure I couldn't do it.

I don't want to romanticise fostering. There are foster parents who neglect, sometimes abuse and fail their young charges. For some children, it erodes their sense of stability and self to live the itinerant life, moving from family to family (some go through dozens in a lifetime) and they grow up bitter and suspicious about the fostering process. Some believe the foster parents are in it for the money or other cynical reasons. But for many more children than we know, the fostering option is far preferable to adoption, and when they finally go out into the world as adults, they remember the best families they passed through, the temporary shelters which became home in their hearts.

When writing my new book Mixed Blessings, I interviewed a number of mixed race children in care. (In some boroughs a disproportionate number of such children end up under local authority supervision.) It was illuminating to hear their stories of living with foster families. A small number of interviewees preferred care homes because there was no pretence there of family life - that is how damaged they were. Only a tiny number wanted to be adopted. Perhaps this was because I was interviewing children who were older than eight and they knew by then that they were never going to be chosen by adoptive parents. Besides, they were still waiting for that day when their real mums or dads would come for them.

For most of my interviewees, foster care was the key, because again there was no demand to commit on either side and yet there were individual relationships and adults who gave their time and care because they wanted to. None of this is statistically valid as I was only interested in individual experiences and choices, but the overall picture was interesting and certainly an endorsement of fostering.

Yet it is only now that Tony Blair seems to be acknowledging this vital input by foster carers, a little too late in my view because it comes when adoption - as a result of the government's lead over the past two years - has now spread like a fervent new religion through social work departments and council chambers across the land. Adoption is fascinating to tabloid newspapers; it appeals hugely to ministers and the prime minister who believe profoundly in a strong, Christian family ethos. The failures of adoption rarely get into public debates; it would wreck our faith in happy endings. Fostering, meanwhile, is a challenge of all that we want to believe about human nature and nurture. There is no final ending, no biological or social family contract, no tangible or visible benefits that The Sun can communicate.

A recent report revealed that more than half of foster carers are not paid a penny. This is unforgivable, appalling, exploitation and it exposes just how we undervalue this essential work.

Fostering has no universal standards, no agreed financial structures, no updated training programmes. Meanwhile, the profile of children in care is changing dramatically - with childhood HIV on the rise, unaccompanied asylum-seeking children in need of homes, more Muslim and Hindu children entering the system with few carers from these communities within the fostering network.

So two cheers for the prime minister for endorsing the work of foster carers, but what is needed is more, and more expensive than pretty words.

Yasmin Alibhai-Brown is a writer and broadcaster.