That data is not accurate, it would have the average UK salary at £44k when the ONS says it is more like £37k
Measures of employee earnings, using data from the Annual Survey for Hours and Earnings (ASHE).
www.ons.gov.uk
However, even with that, average pay is not consistent across the UK so in many regions the average salary is likely to be lower still than £37k.
If you convert that UK salary into Euros you see that average wages in the UK are lower than all of the developed northern European countries, the monthly average would be €3545.