The guidance is reproduced below:

You must tell HMRC if, when you made the claim, you were not eligible for the grant. For example:

• for the first or second grant, your business was not adversely affected.
• for the third or fourth grant, your business had not been impacted by reduced activity, capacity or demand or inability to trade in the relevant periods.
• you did not intend to continue to trade.
• you have incorporated your business since 5 April 2018.

You must also tell HMRC if you:

• received more than we said you were entitled to.
• amended any of your tax returns on or after 3 March 2021 in a way which means you are entitled to a lower grant than you received.

When you must tell HMRC

If you are not eligible and have to pay the grant back, you must tell HMRC within 90 days of receiving the grant.

The process for when and how to tell HMRC is different if amending your return affects your grant amount or eligibility.

If amending your return affects your grant amount or eligibility

You must tell HMRC if there is an amendment to any of your tax returns on or after 3 March 2021 which either: lowers the amount you are eligible for or causes you to no longer be eligible.

If you amend your return before claiming your grant, you must tell HMRC within 90 days of receiving your grant.

If you amend your return after receiving your grant, you must tell HMRC within 90 days of making the amendment.

If you do not tell HMRC you may also need to pay a penalty.

You do not need to tell HMRC if the grant amount you are eligible for is lowered by £100 or less.

If you are unsure if you are affected by these rules, please contact your client manager.