Yesterday, the government announced that the third SEISS grant will be doubled from 20% to 40%, meaning the maximum grant will increase from £1,875 to £3,750.  This grant will have the same eligibility criteria as the earlier SEISS grants, for those who are continuing to trade but are facing reduced demand due to Covid-19 and will cover the three months November 2020 to January 2021. The fourth grant will cover the three months February to April 2021 and is now indicated to be the same as the third grant, although the official guidance still states the level will be reviewed and set in due course.

https://www.gov.uk/government/publications/self-employment-income-support-scheme-grant-extension/self-employment-income-support-scheme-grant-extension