People currently staying in hospitals, police custody, prisons, other institutions who are due for discharge or release in the near future but have no accommodation to go to. What constitutes ‘near future' is a matter of judgement, with the issues obviously being sharper the closer the release date.

These people are an obvious homeless category who will typically not be picked up in the official homeless and in priority need statistics. 

High.  For example, those leaving prisons with no fixed abode would, if they applied, typically be accepted as homeless.  However, despite the widened categories of priority need, many ex-prisoners are still not being classified as priority need, and therefore not entitled to long-term housing from their local authority.

Prisons leavers are likely to represent the most substantial sub-group.  Statistics from the Social Exclusion Unit show that around a third of prisoners about to leave prison said that they had nowhere to stay (Reducing re-offending by ex-prisoners, SEU 2002).

None, given that this group has not yet been discharged/released.

For prisoners, 20,000 over the period of a year and 1,500 at any point in time. There is no data available for deriving any sort of estimated numbers for people leaving other types of institution with no accommodation to go to.

The prison population is around 60,000.  Two-thirds of prisoners stay in prison for less than a year.  Given that around a third have nowhere to go on release from prison (see above), this gives a total of around 20,000 prisoners released each year from prison with nowhere to go.

To put this estimate on a point-in-time basis, make the same assumption regarding ‘near future' as that for evictions, namely that only those due for release within the next 28 days should be counted.  So, the point-in-time estimate is 28/365 x 20,000 = 1,500.

No direct data sources.  Note that the Home Office have, for the first time, started collecting data on the destination of offenders from April 2004 as part of its development of a national accommodation strategy for offenders.