Penalties: late delivery of returns: interaction of flat-rate and tax-related penalties
You can charge both flat-rate and tax-related penalties in relation to the same return. Usually, a flat-rate penalty arises before a tax-related penalty, but it is possible for a company to incur both penalties at the same time.
A company incurs a flat-rate penalty on the day following the filing date (Word 42KB). It usually incurs a tax-related penalty on the day following the expiry of eighteen months after the end of the return period, based on the amount of tax unpaid (Word 41KB) at the 18 month point.
In exceptional circumstances, as explained at COM100110, the filing date may not have been reached at the 18 month point. In that case the tax-related penalty also arises on the day following the filing date.
If, exceptionally, the filing date for the return is more than 18 months after the end of the AP, then the penalty is based upon the tax unpaid at that later date.