There will be further amounts offered under SEISS through to spring of 2021.
At the moment, nobody whose previous profit figures ruled them out will qualify. (For example those with average profits over £50,000.)
Taxpayers who were eligible before may apply, but note that the questions will be different when the next application is made. In particular, there will be a question this time about whether there is less demand/fewer customers since March of this year, for businesses affected.
As before, anyone applying must read the questions carefully and ensure that the declaration is correct at the time it is made. Unless there are specific questions asking about future plans (eg intention to keep trading), SEISS grants are based on the situation at the time the boxes are ticked.
The next, third, claims open during the last week of November via Government Gateway. After several changes, on 5 November the Chancellor announced that the next amount will be 80% of the ‘test profits’, up to a maximum of £7,500. This is the same way that the first (spring 2020) amount was calculated. It is intended to assist during November, December and January. (Details of plans for a further grant expected for February to April 2021 have not been released yet.)
For any taxpayer who qualified before based on their figures, but did not claim, they can make this as their first claim under SEISS if they can now answer yes to all the questions in the declaration.
SEISS grants are part of taxable profits for income tax, but are outside the scope of VAT.
https://www.gov.uk/government/publications/self-employment-income-support-scheme-grant-extension/self-employment-income-support-scheme-grant-extension
https://commonslibrary.parliament.uk/research-briefings/cbp-8879/