Hi John Hopkins,
Thank you for your query.
Grant income that is revenue in nature and relates to trading activities will be subject to corporation tax. If you have received a grant to defray a specific expense, there may be no tax liability even though the income itself is taxable.
If the grant is to be used to offset future expenses, you may find the guidance here useful:
BIM42215 - Deductions: timing: deferred revenue expenditure
HMRC is not able to provide specific tax advice.
If, after consulting HMRC guidance, you still need advice about the accounting and tax treatment of grant income, you will need to speak to an accountant.
Thank you.