Geetika, I am sure the ONS does turnover by industry type so maybe they do a national rate?

This may be industry specific, but page 5 in the below document states labour turnover for all UK employees is 13%

www.greatplacetowork.co.uk/.../The_Biotechnology_Pharmaceuticals_Sector_Insight_FINAL_May_2017.pdf

In reply to Oddrun:

It is so Industry / sector and occupationally- specific that there is a massive spread of different turnover rates, making any overall average for most purposes almost totally useless.

www.eef.org.uk/.../labour-turnover-report
is typical just for engineering / manufacturing