"Self-Employed Income Support Scheme" will pay 80% of average profits over the past three years, up to £2,500 per month, for at least three months, IF your annual profit is not more than £50,000 AND the majority of your income is from self-employment.
If you've made more than that or this has topped up other income, it appears the attitude is 'tough'. If you don't have at least one year's tax return, it appears the attitude is 'tough'. If you haven't yet done a 2018/19 return, which was due in Jan this year, you've got about a month to make one.
There will be a "simple online form" where you apply to HMRC for this. They will then pay the grant straight into your bank account. The grant is taxable.
It might just be applicable to England & Wales, rather than the whole of the UK - certain announcements have been different in Scotland in particular.