The British tax authority (HM Revenue & Customs) must receive the tax return.
For the tax year begins on April 6th of each year to end April 5 of the following year.
In summary:
| SELF ASSESSMENT | DEADLINE |
| Registration for Self-Assessment if you are a self-employed person or an individual, non-autonomous entrepreneur, or a partner or partnership registration | October 5th |
| Tax return | By midnight on October 31st
|
| Online tax declaration | By midnight on January 31st |
| Payment of taxes on the basis of the declaration | By midnight on January 31st |
It is possible to oppose if the delay is attributable to a reasonable cause.