Although PAYE has been with us since the 1940s, one surprising aspect was that, until now, there have never been provisions enabling HMRC to charge interest on late payments of PAYE during the tax year. Interest only becomes payable when there was PAYE still outstanding as at 19 May following the end of the tax year.
This is to change with effect from 2010/11 onwards. New provisions are being introduced, under which HMRC may charge penalties any late-paid PAYE payments, during the tax year. This also applies to payments under the CIS scheme.
See details of the new PAYE late payments on GOV.UK's website.