Almost every political figure in Britain believes ‘we need more social mobility’ and wants social policies to achieve it. Suppose they are right, and that ‘mobility rates are low and falling’ (they are not right, but just suppose they were): what would happen if their policies worked?

First, more people would have the ‘requirements’ (qualifications, aspiration, cultural capital) to compete for the stock of ‘good’ jobs. These good jobs are presently filled by other people, who would have to be displaced – made downwardly mobile – to make room for the potential newcomers. If some of the present incumbent families did cling on to their advantages (because they also have the requirements to occupy the good jobs, and are doing them well), would some of those newly qualified with the requirements then not be upwardly mobile and so become doubly disillusioned by their lack of achievement? Even if there were to be some increase in upward mobility, what would happen to those who, despite new policies, did not acquire the requirements and remained trapped in ‘poor’ jobs, immobile at the bottom of the heap?

‘Ah!’ say the politicians, ‘but the number of highly skilled jobs is increasing, so making greater room at the top’. There is some truth in this, but the increase would have to neatly match the inflow of the newly qualified. And it would have to be a very large increase. Previous studies indicate that an expanded number of new good jobs gets shared out more or less equally between the children of families already holding good jobs and those from families who had less good jobs.

What our politicians really want is greater upward mobility. They want less immobility among those who start at the bottom of the social heap and fairer access to managerial, professional and elite positions at the top. But what they have failed to grasp is that ‘more social mobility’, by both definition and practical outcome, also means greater downward mobility. You can't have one without the other. If we are to understand ‘mobility’, we need to look at the whole picture.