Whats the average length of hospital stay in the UK?

All other things being equal, a shorter stay will reduce the cost per admission (about £400 a day, much more on ICU etc) and shift care from inpatient to less expensive outpatient settings:

• Home. If independent, free!
• Carers. For one hour 4x a day (£20 an hour) = approximately £550 per week
• Residential/nursing home = £700-800 a week.

Other resource

The OECD has data which compares length of stay in developed countries. As you can see the UK is mid-table at 6 days, indicating we are an averagely efficient system.