After the initial decision has been made on your claim for tax credit, it can be revised if your circumstances change. Remember that if you do not report some changes in time, it could lead to a penalty fine or to you losing tax credit. You can also ask for a revision if the Inland Revenue made a mistake in its initial decision.
If you think the initial decision is wrong or your claim is refused altogether you do have the right to appeal. If you disagree with a revised decision you can also appeal against this.
After a final decision has been made on your claim at the end of the tax year, the Inland Revenue can still enquire whether your entitlement was correct. Any decision made as a result of such enquiries carries the right of appeal. If you can show an official error occurred, it can be revised instead.