The number of patients waiting in Scottish hospitals beyond the end of treatment has increased in the past year.

There were 606 delayed discharges in January, an increase from 492 in the same month last year, according to NHS statisticians at ISD Scotland.

Of those, 83 patients waited more than six weeks to leave, up from 79 in January 2009.

The problem arises when patients have to wait for necessary care, support and accommodation arrangements to be put in place.

Although up over the past year, the recent figures showed a fall from a peak in October.

The figures are dramatically down on previous years. In January 2007 there were 606 patients waiting more than six weeks to leave hospital.

Public Health Minister Shona Robison said: "It's very encouraging to see the number of patients inappropriately delayed in hospital has fallen since the last census, as has the number of patients delayed more than six weeks.

"This census was held in January this year, when health and social care staff across Scotland were going the extra mile to cope with increased activity because of the severe weather. Their efforts were remarkable and helped to maintain services for some of our most vulnerable people.

"These figures do illustrate good progress in recent years - and compared favourably with the 606 patients delayed in hospital more than six weeks in the January 2007 census.

"Nevertheless, zero delayed discharges is a standard that should be maintained at all times. It has been achieved before and we want to see it achieved again."

Labour health spokeswoman Jackie Baillie said: "I am deeply concerned that bed blocking continues to be a problem in Scottish hospitals and has increased since last year. This puts unnecessary pressure on doctors and nurses.

"Delayed discharges are a problem because any patient, particularly if elderly, has a higher risk of hospital acquired infection for every unnecessary day they spend in hospital.

"This failure represents another broken promise for the SNP. The Health Minister Shona Robison promised that the figure would remain at zero but has made no real progress in delivering this pledge."

The problem reached its peak in 2001 when the figure stood at 2,162 before falling steadily to zero in April 2008.

Separate health statistics released today showed that 99.9% of inpatients and outpatients are being seen within the 15-week national waiting time target.