From 6 April 2015 employers will no longer have to pay Class 1 secondary National Insurance contributions on earnings up to the Upper Secondary Threshold (UST) for employees under 21 years.
The Abolition of employer National Insurance contributions for under 21’s section of GOV.UK has been updated and now includes more detailed guidance for employers, plus detail on the new category letters and rates.
Read more: https://www.gov.uk/government/publications/employer-national-insurance-contributions-for-under-21s/abolition-of-employer-national-insurance-contributions-for-under-21s-employer-guide–2