You cannot claim relief until the company sends you a form EIS3. (See Part 2 for an explanation of what the company has to do to put itself in that position.) If you invest through an Approved Enterprise Investment Scheme (EIS) Fund you will receive a form EIS5; see paragraph 1.6.
Your claim can be made on the Self Assessment tax return for the tax year in which the shares were issued. If the shares were issued in a previous year, and/or if the claim is for capital gains deferral relief, the claim part of the form EIS3 must also be completed and sent to your tax office.
If you have an EIS3 for a year for which you have not yet received a tax return, you can request a change to your PAYE tax code, or an adjustment to any Self Assessment payment on account due. You will still have to make the claim itself on your tax return when you get it.
Claims to relief can be made up to five years after the first 31 January following the tax year in which the investment was made.