How to apply for the third and fourth SEISS grant

With applications for the second Self-Employed Income Support grant now closed, The Chancellor has announced an extension to the scheme via a third and fourth grant.

We now know that the third grant will be calculated as 80% of trading profits, capped at £7,500 and will cover the period November 2020-January 2021.
For reference, the first grant was 80% capped at £7,500 and the second grant was 70% at £6,750.
There is no official detail on the fourth grant except that it will cover the period February 2021-April 2021.

Eligibility: If you were eligible for the first two grants, you will be eligible for the third and fourth grants. As a refresher, the criteria is that you must have submitted a tax return for 2018-19 and over 50% of your taxable income has to be from a trade. Applications must declare their business has been negatively impacted by Covid-19 and that they do intend to continue to trade.
It has advised that you only claim the grants if your business has actually been adversely affected by Covid-19. HMRC has published guidance on what counts as adversely affected here

When and how to claim: Applicants are advised to used the same claim portal used for the first two grants. HMRC will open the portal on the 30th November. As with the first two grants, applications must be made by the tax payer and must not, in any case be made by accountants on behalf on their clients.

Key details: Please note that all instances of the grant are fully taxable and will be added to your 2020/21 tax return. In addition to this, please be aware of fraudsters who will be looking to target applicants. As a general rule, official HMRC emails will never request you click on a link.